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Dicotyles Hesperius, sp. nov.

A new and interesting small Suilline mammal is well represented by a portion of a right upper jaw, with the last premolar, and the succeeding three molars, all in excellent preservation. The teeth indicate an individual. fully adult. They have nearly the composition of those of the modern Peccaries, and evidently belonged to the same, or a closely related, genus. The species is well marked, and was apparently not more than one half the bulk of Dicotyles torquatus. The crowns of the molars have a more rhombic outline than in that species, and a more distinct valley between the anterior and posterior pair of cones. The basal ridge is also more strongly developed, especially on the outer margin, where it is continuous. In other respects the composition of these teeth is very similar in the two species. The last upper premolar in the present specimen, however, differs widely from the corresponding tooth in any of the known Peccaries, living or fossil, resembling most nearly in its composition the second premolar of D. torquatus. The latter has, however, the single posterior cone distinct, while in the species under consideration it is connate with the anterior outer tubercle. The upper dental series is here somewhat curved outwardly, and not on a line, as in the living Peccaries.

Measurements.

Length of part of upper jaw with four posterior teeth, 19 lines.
Length of same, with three molars,.

Antero-posterior diameter of last upper molar,.
Transverse extent of same,-

15.2

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5.6

66

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66

Antero-posterior diameter of penultimate upper molar, 54

This specimen, for which the writer is likewise indebted to Rev. Mr. Condon, is from the same locality and geological horizon as the species last described.

Hypsodus gracilis, sp. nov.

This species was about the same size as Hypsodus paulus, a small mammal described by Dr. Leidy from the lower Tertiary basin in Wyoming, and supposed by him to indicate an animal probably allied to the suilline family.* It may readily be distinguished from that species, especially by the first true molar of the lower jaw, which is proportionally narrower in front, and broader at its posterior margin. There is also on this tooth a strong external basal ridge, and, at the anterior inner angle, a prominent projection, which is wanting in H. paulus. The lower jaw is, moreover, deeper and more compressed in the region of the premolars.

* Proceedings Philadelphia Acad. Nat. Science, 1870, p. 109.

Measurements.

Length of part of lower jaw containing first molar and

last two premolars,

Antero-posterior diameter of first lower molar,
Transverse diameter through posterior lobe,.

Antero-posterior diameter of last lower premolar,..........

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The specimens representing this species at present were found by the writer, at Grizzly Buttes, Wyoming.

Limnotherium tyrannus, gen. et sp. nov.

A somewhat larger pachyderm, but distantly allied apparently to the two small species last described, is represented by the anterior portions of two united lower jaws, with several teeth, and a few other fragmentary remains. These specimens appear to indicate a genus quite distinct from any hitherto known, but additional remains will probably be required to determine its exact affinities. The teeth of the lower jaws are twenty in number, and form an uninterrupted series, which may be divided as follows:-Incisors 2-2, canines 1-1, premolars 4-4, molars 3-3. The incisors are small, and crowded together. The canines are large, nearly round at the base, and evidently formed most efficient weapons. The first and second premolars had but a single fang. The two anterior molars are in excellent preservation, and have their crowns composed of four principal cones. The first is at the anterior outer angle; the second just behind this, on the inner margin; the third at the outer posterior angle; and the fourth and smallest at the inner posterior corner, separated from the others by a deep pit. Each molar has a rudimentary double tubercle on the anterior margin, and a moderate basal ridge, except on the inner side.

Measurements.

Length of dental series of lower jaw,
Antero-posterior extent of three molars,.
Transverse extent of four incisors, -

Length of symphysis, ...

Depth of lower jaw below last molar,

Depth below last premolar,..

Antero-posterior extent of first lower molar,

Transverse diameter of same,.

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The specimens here described were found by the writer near Dry Creek, Western Wyoming, in deposits which are probably of Upper Eocene age.

Limnotherium elegans, sp. nov.

A diminutive mammal is represented in our collections by portions of two lower jaws, with several teeth, which have so

nearly the composition of those in the preceding species that they undoubtedly belong to the same, or a nearly related, genus. One of these specimens contains the last premolar, and the two succeeding molars. In the latter, the two anterior cones form a transverse pair, and are not oblique as in the larger species. The posterior pair of tubercles, also, are nearly on a transverse line.

Measurements.

Length of fragment of lower jaw, enclosing last premo

lar and three molars,

Antero-posterior diameter of second lower molar,
Transverse diameter of same,..

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The only two specimens of this species now known were found by the writer at Grizzly Buttes, near the base of the Uintah Mountains, in Wyoming.

Yale College, New Haven, June 5th, 1871.

ART. IX.

Contributions to Chemistry from the Laboratory of the Lawrence Scientific School. No. 16.-On the Atomic Weights of Cobalt and Nickel; by RICHARD H. LEE.

THE atomic weights of cobalt and nickel have long been subjects of controversy, but though much time and labor have been spent upon them, the results arrived at are not as satisfactory as could be desired."

Under these circumstances Prof. Gibbs suggested to me a new investigation of the subject. Before giving an account of my own methods and results, I will state briefly those of other chemists. Rothhoff,* in 1826, first endeavored to ascertain the atomic weights of cobalt and nickel. He determined the amount of chlorine in the respective chlorides, by means of silver, and from a single analysis of each chloride, obtained for cobalt the equivalent 29.55, and for nickel the equivalent 29.60. the methods of separating the two metals were at that time imperfect, and as but a single analysis was made in each case, Rothhoff's results can hardly be considered as deserving of confidence.

As

Erdmannt and Marchand, in 1852, determined the atomic weight of nickel by reducing nickelous oxide in hydrogen. Their results varied between 29.1 and 293, and they regarded the lower number as more probably correct. It seems at least possible that the nickel they employed contained traces of cobalt. The subject was again taken up by Schneider‡ in 1857.

* Poggendorff's Annalen, vol. viii, p. 184-5.
Annalen der Pharmacie, vol. lxxxii, p. 76.
Poggendorff's Annalen, ci, p. 387.

Pure metallic cobalt was prepared by igniting chloride of purpureocobalt in hydrogen. The metal was then dissolved in chlorhydric acid and precipitated by sodic carbonate. The carbonate was washed, and then digested with oxalic acid, the resulting oxalate again washed, burned in a current of oxygen and the oxide reduced by hydrogen. In other portions of the oxalate the carbon was determined by combustion with cupric oxide.

The following table gives a summary of the results obtained:

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Determinations of the atomic weights of cobalt and nickel were also made in 1857 by Marignac.* Cobaltous sulphate was purified by repeated crystallization and a weighed quantity of the salt heated so as to expel the acid. The resulting oxide was then heated with a known weight of silicate of lead so as to expel the excess of oxygen over and above that required to form cobaltous oxide Co0. The results obtained varied between 29.32 and 29.38.

Crystallized cobaltous chloride dried at 100° was found to retain one atom of water. Three determinations of the chlorine in this salt by means of silver, gave for the atomic weight of cobalt 29-42 to 29:51. Anhydrous cobaltous chloride was obtained by heating the crystallized salt with sal-ammoniac, in a current of dry chlorine or dry chlorhydric acid gas. The salt almost always however left a slight residue insoluble in water. Five analyses of the anhydrous salt gave results varying from 29.36 to 29.42.

In 1859 Dumast turned his attention to the subject. Perfectly pure metallic cobalt was dissolved in nitro-muriatic acid, the solution evaporated to dryness with frequent additions of chlorhydric acid, and the cobaltous chloride submitted to a red heat. In a second preparation from a different sample of metal the chloride was dried in vacuo. In this manner the following results were obtained:

* Bibliothique Universelle de Geneve, Nouvelle series, vol. i, p. 373.
Ann. de Chimie et de Physique, 3d series, vol. lv, p. 148.

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The mean of these five determinations is 2954. In all cases the chloride was dissolved in boiling water and the solution allowed to cool before precipitating with AgNO,. The argentic chloride was reduced in hydrogen. The method employed for the preparation of pure cobalt is not stated.

Russell* determined the atomic weights of cobalt and nickel in 1863. Pure metallic cobalt was prepared by igniting chloride of purpureocobalt in hydrogen. The metal was dissolved in nitric acid and the solution evaporated and strongly heated. The black oxide obtained was ignited in a current of carbonic di-oxide, by which it was converted into light brown cobaltous oxide CoO, which was then reduced by pure hydrogen. Omitting two trial experiments, the results obtained were as follows:

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