MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 
35 
is very short hat quite stout and wholly unarmed, while the single terminal segment or ramus is 
minute, scarcely longer than broad, and tipped with three spinules. The telson, as seen from above, 
is rectangular, nearly as broad as long; the posterior margin has a very shallow sinus in the 
middle, each side of which is armed with several slender spines. The other appendages are suf¬ 
ficiently well shown in the figures. 
A smaller female, about 3.5 mm long, differs very slightly from the last. The flagella of the 
antennulse are each composed of ten segments and those of the antennae of four. In the second 
pair of legs the propodus is relatively not quite as large, is a very little narrower, and the palmary 
margin has one or two less spines on the outer side; all characters of a slightly less mature 
specimen. 
The three other specimens are very small, and I have not been able to determine the sex of 
any of them. They may be either young males or immature females. One of these, about 2.7 mm 
long, differs considerably from the larger specimens, but only in such characters as immature 
specimens usually differ from the adults. There are only eight segments iu the flagellum of the 
antennula and four in that of the antennae. In the first pair of legs the propodus is a little more 
slender than in the adult, the palmary margin is not quite as oblique, and is armed with one or 
two less spines on each side. The second pair are only very slightly larger than the first, and’of 
course very much more slender than in the adult. The propodus is narrower in proportion and 
scarcely wider than the carpus. The palmary margin is less oblique, not longer than the posterior 
margin, and is armed with fewer spines on each side. The first and second pairs of caudal stylets 
and the telson are armed with a few less spines. 
I have been unable to discover even rudimentary eyes in any of the specimens. 
This species agrees with Bates’s description of the typical species of the genus in having the 
posterior caudal stylets “ unibranched,” and thus differs from the following species which we have 
referred to the genus, although in Bates’s species the terminal segment or ramus of the stylet is 
as elongated as the outer ramus in C. gracilis and 0. paekardii. 
In the structure and size of the posterior caudal stylets, in the stoutness of the second 
pair of legs, and in wanting eyes, this species approaches C. tenuis , from wells at Middle- 
town, Connecticut, to which it is apparently more nearly allied than to any of the described 
American species. The G. tenuis is, however, a wholly distinct and quite different species. I 
know of no species with which this is closely enough allied to make its affinities of any value on 
the question of the origin of the cave fauna (S. I. Smith). 
Figs. 1 to 4.— Crangonyx vitreus, female, S.2 mm long: 1, lateral view, enlarged 20 diameters; 
2, one of the first pair of legs seen from the outside, enlarged 48 diameters; 3, one of the second 
pair of legs, enlarged 48 diameters; . 4, terminal portion of the abdomen, side view, enlarged 48 
diameters; a, telson; 6, posterior caudal stylet; c, second caudal stylet; d, first caudal stylet. 
This species was not uncommon in the pools of Mammoth Cave, occurring in Richardson’s 
Spring and Wandering Willie’s Spring. It has the habits of Gammarus, scooping a furrow in the 
mud of the bottom of the pools in which it lives. 
Crangonyx paokardii Smith. PI. Y, figs. 5 to 11. 
Crangonyx vitreus Packard, Fifth Atm. Kep. Peab. Acad. Sci., Salem, 95. July, 1873. 
Not Stygobromus vitreus Cope, Amer. Naturalist, vi, 422, 1872. 
This species is so closely allied to Crangonyx gracilis that it might readily be mistaken for it 
were it not for the peculiar structure of the eyes. The eyes of G. gracilis are composed of a few 
facets, and are abundantly supplied with black pigment. In all the specimens of G. paekardii 
which I have seen the eyes are observable with difficulty, the black pigment being wholly wanting. 
The specimens received at first were very badly preserved, and I then thought the absence of the 
pigmeut might be due to this fact; but subsequent examination of more perfect specimens shows that 
this cannot be the case, and that the eyes are, in life, undoubtedly wholly without black pigment. 
The eyes are scarcely, if at all, observable in the ordinary alcoholic specimens, but when rendered 
translucent by immersion in glycerine the structure of the facets is distinctly observable, as shown 
in Fig. 5. As observed by Dr. Packard, the flagella of the antennulse of C. paekardii are a little 
shorter, and usually contain four or five segments less than in C. gracilis, , but this is an uncertain 
