NO. 1507. FRESH-WATER AMPHIPODA—WECKEL. 35 



First uropods projecting backward beyond the second pair, and the 

 second beyond the third; third pair consisting of a peduncle and a 

 single small ramus; peduncle more than twice as long as broad, fur- 

 nished with a few spines, and produced distally on the inner side into 

 a short, blunt process furnished at the tip with a small spine; ramus 

 about two-thirds the length of the peduncle, provided with a few 

 spines. Telson cleft three-fourths the distance to the base, projecting 

 beyond the third uropods, lobes diverging toward the tip, each armed 

 distally with three or four spines. 



Length, 9 mm. 



Type locality. — Macon, Mississippi, 



This species differs from the other members of the genus Eucran- 

 gonyx in the absence of the rudimentary inner ramus of the third 

 uropods. In all other characters, however, it so closely resembles the 

 species of this genus that it seems best to retain it in Eucrantjonyx 

 rather than to place it in a new genus. 



EUCRANGONYX PACKARDII (Smith). 



Crangonyx packardii Smith, 3Ieiii. Nat. Acad. Sci., I\', 1888, pp. 34-36, pi. v, 

 fig?. 1-11. 



The following description, with iigures, is taken from Memoirs 

 National Academy of Sciences, where the species is described by 

 Prof. S. I. Smith as Crangonyx pachirdiL 



This species iH so closely allied to Crangonyx gracilix that it might readily be mis- 

 taken for it Avere 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 C. packardii 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 thought the absence of the pigment might 

 be due to this fact; but subsequent examination of more perfect specimens shows 

 that this can not be the case, and that the eyes are in life undoubtedly w" holly with- 

 out black pigment. The eyes are scarcely, if at all, observable in the ordinary alco- 

 holic specimens, but when rendered translucent by immersion in glycerin the 

 structure of the facets is distinctly observable, as shown in fig. 5. As observed by 

 Doctor Packard, the flagella of the antennuhE of C. gradiis are a little shorter, 

 and usually contain four or five segments less than C. gracilis, but this is an uncer- 

 tain character, and some specimens of C. gracilis from Lake Superior actually have 

 only one or more segments than the subterranean species. In the antennte there are 

 no constant differences. There are some very slight differences in the first and sec- 

 ond pairs of legs; especially in the females, but not greater than usually exist in the 

 individuals of a single species in allied genera, and any large series of specimens 

 would undoubtedly show^ all the intermediate forms. In the third to the seventh pair 

 of legs there is a constant difference in all the specimens examined, the spines being 

 more numerous, longer, and more slender in C. gracilis. The spines upon the first 

 and second caudal stylets are a little shorter and more obtuse in C. puck-ardii than 

 they usually are in C. gracilis; otherwise there is no difference in the caudal stylets 

 and telson. 



These differences are all such as very naturally lead to the supposition that this 

 subterranean form has been derived from the C. gracilis at no very remote period, 



