142 bulletin: museum of comparative zoology. 



The mammae are two on eacli side, as in other members of the 

 genus, one pair pectoral, one abdominal, situated well up on the sides. 

 The naked soles of both fore and hind feet are granulated, but like 

 those of C yj/r/u'/^^i/w, have three larger pad-like areas on the palms, 

 with on the fore feet, two additional ones nearer the carpus. 



The measurements in the flesh are: — ^ total length 395 mm.; tail 

 176; hind foot with claws, 45 long, by 14 in greatest width of palm; 

 ear from meatus 19, its greatest transverse width 14.5. 



The ^Mscera were somewhat macerated, but in so far as could be 

 ascertained, seemed to differ in no important way from the soft parts 

 of C. melanurus as described by Dobson (1884). The coecum seemed 

 relatively larger, about the length of the body-cavity, and distinctly 

 sacculated (about 115 mm. long). The body-cavity posterior to the 

 diaphragm is large to accommodate the intestinal mass. The large 

 ovoid kidneys are conspicuous, and as in C. pUorides have an elon- 

 gate oval adrenal body close to the anterior end of each. The liver 

 is like that of C. melanurus except that it appears to lack the small 

 secondary lobe at the base of the main anterior lobe of the left side. 

 This lobe is present in both C melanurus and C. pUoridcs. As first 

 descril)ed by Say (1822), the liver in the latter species is remarkable 

 on account of its being minutely divided into separate glandular 

 masses closely appressed, so that exteriorly the main lobes have a 

 reticulate appearance. This character, so evident in C. piloridcs, is 

 quite absent in the livers of C. melanurus, C. ijrehensilis, and C. nana, 

 which present the usual solid structure. The small thoracic cavity 

 is bounded posteriorly by the diaphragm which reaches ventrally the 

 10th rib, and dorsally extends back as far as tKe 12th. The lungs 

 agree in their general form with those of C. melamirus and C. piloridcs 

 as described by Owen (1832). 



In the characters of the skull, C nana is in several ways the most 

 primitive of the genus, with certain striking resemblances to the 

 spiny-rats (Echim^dnae). Thus the brain-case is much less prolonged 

 and rounder in profile than in any of the other species. The orbit is 

 very large for the genus, larger than the antorbital foramen, with a 

 lighter zygomatic arch, in decided contrast to adults of the other 

 species, in which the height of this foramen equals (C. p)rchensHis 

 and C. melanurus) or exceeds (C. pilorides and Geocapromys (the verti- 

 cal diameter of the orbit. A third point of resemblance to the spiny- 

 rats is in the narrow ledge or beading overhanging the orbit and 

 temporal fossa as far back as to include the upper edge of the squamosal 

 process. That these characters are primitive is indicated by the fact 



