NYCTINOMUS TENUIS. 



femoral membrane. The body is deep brown, inclining to sooty black; intense, 

 above, and grayish underneath. The fur is extremely soft and delicate, closely 

 arranged, and of uniform length throughout. 



DIMENSIONS. 



Inches. Lines. 



Length of the body and head, from the nose to the root of the tail.... 2 5 



the tail '■ 1 4 



Expansion of the wings 12 6 



Length of the arm and fore-arm 2 6 



the phalanges of the middle finger 3 3 



the bones supporting the tluimb 3^ 



the posterior extremities 1 1 



Breadth of the membrane of the wings at the narrowest part, oppo- 

 site to the junction of the ariu and fore-arm 1 



Greatest expansion of the ears on the summit of the head 9 



The general form and the organization of the Nyctinomi are in perfect coitc- 

 spondence with their habits, and mode of life. Of all the various VespertUionidee 

 which I have examined, these have the greatest expansion of wing ; a property 

 which, united to a tapering body, terminated by a long and gradually attenuated 

 tail, enables them, perhaps with more facility than other animals of this order, 

 to dart through the air in rapid flights, and abruptly to change their direction, 

 in the pursuit of minute objects. The Nyctinomi have also a system of denti- 

 tion, which among all the Vespertilionidee deviates farthest from that of the 

 Pteropi. In the latter, which feed on fi-uits and vegetables, the grinders have an 

 almost even and regular crown, divided by one simple longitudinal furrow ; in the 

 former, it is complicated to such a degree, that it is difficult, by words, to describe 

 it distinctly. Great care has therefore been taken, in the Plate which illustrates the 

 generic character of Nyctinomus, to exhibit an accurate view of the various points, 

 grooves, and processes of the grinders. To this I therefore refer in illustration of 

 their description. The canine teeth are remarkable in both jaws: in the upper, they 

 present interiorly a very sharp cutting edge ; in the lower jaw, they are of uncommon 

 size, greatly distended at the base, and provided with a strong, obliquely diverging 

 process, resembling a thorn, which forces the front teeth in an obhque direction 

 forward. This peculiar structure serves to prevent the escape, and to secure in the 

 interior part of the mouth, the minute insects which are seized in the rapid move- 

 ments of the Nyctinomi, untU they can be conveyed to the back part of the mouth, 

 where the grinders furnish a most effectual apparatus for their immediate destruction. 



