Say on Isodon Pilorides. 227 



Fig. 6. One of the lateral tubercles of the thorax, highly magni- 

 fied;, which supports the double eye. 



Note. — The author having used the term machoire, to signify sometimes 

 maxilla and sometimes mandible, as also the words levres, when the maxilla, 

 and menton, when the labrum is obviously intended, the preceding alterations 

 in the translation of his paper, are absolutely necessary. 



Art. XXVII. On a Quadruped belonging to the Order 

 Rodentia. By Thomas Say.* 



In the valuable collection of the Philadelphia Museum, there is 

 the preserved skin of a mammiferous quadruped, exhibiting at 

 first view the appearance of a gigantic rat, somewhat larger than 

 a rabbit, and known in that institution by the name of long-tailed 

 Cavy ; a designation founded on the belief of its being either the 

 Chloromys acuchi, or an undescribed analagous species. 



It was brought to the museum more than twenty years ago, 

 either from South America, or one of the West Indian Islands, and 

 from that period to the present it has been open to the inspection 

 of the curious. 



More recently a living specimen of the same animal was pre- 

 sented to the museum, which afforded the proprietors an opportu- 

 nity of becoming acquainted with the habits of the species in a 

 state of domestication. 



I shall, in the first place, state the characters of a new genus, 

 which I have constructed for this animal, and afterwards note its 

 difference from, and correspondence with, other genera, to which 

 it seems allied. 



Order.— RODENTIA. Genus.— ISODON. 



Artificial Character. 

 Clavicles perfect ; molares sixteen, prismatic, not divided into 

 radicles ; toes divided. 



* Extracted from a paper in the Journal of the Academy of Natural Sciences 

 of Philadelphia ; vol. ii. p. 330. 



