Zoological Society. 229 



also ; in the molar teeth of the lower jaw the fold of enamel between 

 the first and second portions of the bony lamince of each tooth does 

 not reach quite to the outer edge, and the two portions of bone ap- 

 pear therefore to be only partially separated. The direction of the 

 parallel lamince of all the molar teeth is not at right angles with the 

 line of the maxillary bones, but inclining obliquely from without 

 backwards. 



"The length from the atlas to the end of the tail is 11 inches 

 rVths ; cervical vertebra 7, dorsal 13, lumbar 6, sacral 2, and cau- 

 dal 23. The scapulce are small, measuring 1 inch from the exter- 

 nal angle to the articulation with the humerus, the spine is but 

 little elevated, the acromion ample, the clavicles perfect ; length of 

 the humerus 1 inch -j-Vths, , the bone strong and furnished with an 

 elongated crest descending from the head ; from the olecranon to 

 the carpal articulation 1 inch Vo-ths, the ulna and radius firmly an- 

 chylosed throughout the distal half of their length ; thence to the 

 end of the longest of the five toes -Aths of an inch. The ribs 13 pairs. 

 The bones of the pelvis slender and elongated ; from the crest of the 

 ilium, which is but little produced, to the inferior edge of the 

 ischium is 1 inch ^ths ; the ossa pubis, slight in structure, advan- 

 cing but little, the symphysis elongated, and the obturator foramen 

 of large size. The femur is straight, strong and smooth, and mea- 

 sures 1 inch T^-ths ; the tibia 2 inches ^ths ; thejibula is complete 

 and forms the external malleolus ; from the os calcis to the end 

 of the longest toe 2 inches -rVth; the toes four in number, of which 

 the outer one is the shortest, the third from the outside the longest, 

 the second and fourth equal. 



" In the published observations before referred to I stated that 

 the Chinchilla appeared to be closely allied to Mr. Brookes's new 

 genus Lagostomus, and the character of the skeleton of the Chin- 

 chilla compared with the figure and description of Lagostomus in 

 the 1st part of the 16th volume of the 'Transactions of the Lin- 

 nean Society' confirms the general similarity. Still, the more 

 complicated structure of the teeth, and the existence of an additi- 

 onal toe on each of the feet, require for the Chinchilla the generic 

 distinction claimed for it by Mr. Bennett and by Mr. Gray. 



" The resemblance of the skeleton of the Chinchilla to that of 

 the Jerboa is also remarkable, particularly in the form of the head, 

 in the excessive development of the auditory cavities, and the 

 small size of the anterior extremities compared with the hind legs.'* 



Mr. Yarrell having concluded the reading of his Notes, it was 

 remarked that MM. Isidore Geoffroy-Saint-Hilaire and Dessalines 

 d'Orbigny had proposed, in the * Annales des Sciences Naturelles' 

 for November 1830, the creation of a new genus, Callomys, to in- 

 clude the Chinchilla and the Viscaccia. The latter animal is the 

 Dipus maximus, De Bl., and consequently the type of the genus 

 Lagostomus, described by Mr. Brookes in a paper read before the 

 Linnean Society in 1828, and published in the Transactions of that 

 body in 1829, in which the system of dentition and the osteology 

 are treated of in detail. The Chinchilla, long known in commerce 



but 



