226 Bulletin American Museum of Natural History. [Vol. V, 



The skulls of course vary greatly according to age, in propor- 

 tion of parts as well as in size. There is also considerable indi- 

 vidual variation, especially in respect to the posterior extension 

 of the nasals. These in some examples pass but little beyond 

 the fronto-maxillary suture, while in others they extend much 

 further. There are also minor variations in other parts, as shown 

 by the following table of measurements of eight adult skulls : 



Cranial Measurements. 



The tendency in these animals to lose the tails renders an ex- 

 amination of the posterior portion of the vertebral column of the 

 tailless examples a matter of interest. Fortunately this portion 

 of the skeleton of two of the tailless specimens was preserved, 

 and shows that the amputation occurs at the second vertebra be- 

 hind the posterior border of the pelvis, or just behind the fifth 

 caudal. The first four caudals are normal in size and propor- 

 tions, and appear to be in a healthy condition ; the fifth caudal 

 is abnormal, the posterior third or half having apparently been 

 lost by absorption. A further interesting fact was noted in skin- 

 ning the specimens in which the tail was still intact, namely, its 

 easy separation at the fifth caudal vertebra, in several specimens 

 the tail breaking at this point in the process of skinning. 



The genus Echimys is now for the first time positively shown 

 to be an inhabitant of the Island of Trinidad. It is true that 

 " Echimys, sp." is entered in Mr. Thomas's list, but it is given 



