NVCTTNOMUS TENUIS. 
The neck is of moderate length, and robust; and the body is broader at the thorax, 
and gradually attenuated towards the posterior extremities. It is densely covered with 
a very delicate fur, which also forms a regular border along the sides, from the 
shoulders to the vent. The breasts and sexual organs are completely hid from view 
by the close hairy covering. The expansion of the wings is comparatively greater 
than in the other Vespertilionidae. The bones of the arms, and the phalanges being 
greatly lengthened and very slender, the form of the wings is consequently narrow, 
oblong, and sharp towards the extremity. This indeed is the general character of 
the Nyctinomi ; but it exists in a greater degree than in the species from Egypt and 
Bengal, and from this character the specific name is derived. The Nyctinomus 
tenuis is also peculiarly distinguished by the narrowness of the membrane of the 
wings near the body, opposite to the junction of the arm and fore-arm, from another 
Javanese species contained in our collections, which 1 have denominated Nycthionius 
diJatatus, the characters of which I shall concisely define at the end of this article. 
The lower extremity of the os humeri is provided at its articulation, with a 
cartilaginous appendage of an irregular form, from which a very delicate tendon 
passes, parallel to the arm, towards the shoulder. The thumb, comparatively with 
other Nyctinomi, is long, and provided as usual with several bones for its support ; 
the claw is very minute. The index has three phalanges, of which the two exterior 
are scarcely distinguishable by the naked eye. The middle finger has four, and eacli 
of the others three phalanges : the extreme ones are very slender and delicate. The 
membrane is delicate, transparent, and dotted on each side of the body towards the 
arms, exhibiting a character which exists in a certain degree perhaps in all Nyctinomi, 
and which lias suggested the name of acetabulosus for Commerson's species ; it passes 
over the carpus to unite itself with the interfemoral membrane. The latter is consi- 
derably tapering in the middle; having several deep folds near the posterior border, 
and being provided with several bundles of muscular fibres stretching transversely 
over it. 
The tail is long, slender, and extremely delicate at the extremity ; of about 
nine cylindrical vertebra wluch compose it, three only are enveloped in the mem- 
brane : more than one half of this organ is thus detached. The feet are provided 
with five toes of nearly equal length, each of which has a strongly compressed and 
sharp claw : numerous strong bristly hairs are scattered on the feet, spreading irre- 
gularly in all directions. 
The colour of the transparent membrane of the wings is sooty black, with a 
slight tint of brown : it is more intense in the ears, the nose, the tail, and the inter- 
