MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 35 



is very short but 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 

 antennulaB are each composed of ten segments and those of the antennse 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 specimeus, but only in such characters as immature 

 specimens usually differ from the adults. There are only eight segments in the tiagellum of the 

 antennula and four in that of the antennse. 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 G. gracilis and C. paclcardii. 



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 G. 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, 5.2 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; b, 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 packakpii Smith. PL V, figs. 5 to 11. 



Crauyonyx vitreus Packard, Fifth Ann. Eep. Peab. Acad. Sci., Salem, 95. July, 1873. 

 Not Styyobromut 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 C. gracilis are composed of a few 

 facets, and are abundantly supplied with black pigment. In all the specimens of G. paclcardii 

 \ inch 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 

 pigment might be due to this fact ; but subsequent examination of more perfect specimeus 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 specimeus, 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 antenuulse of G. paclcardii are a little 

 shorter, and usually contain four or five segments less than in G. gracilis, but this is an uncertain 



