34 
MEMOIRS OP THE NATIONAL ACADEMY OP SCIENCES, 
A. communis, only narrower, and with longer set®, especially the terminal ones. The first antenn® 
are fourteen-jointed, while the olfactory rods and auditory bristles are essentially as in A. communis. 
Mr. Forbes writes me that “there is some room for supposing that my A. intermedins is a 
dwarf form of A. communis; but I think no one could suppose that A. brevicauda was other than 
a distinct species. It occurs in the hill country of southern Illinois, and probably also farther 
south.” 
Asellus brevicauda Forbes, l. c., p. 8. 
In this form, which lives in clear rocky rills in Illinois, which is described in detail by Mr. 
Forbes, the first antenn® are fifteen-jointed. The auditory bristles are well developed, and there 
are five on the end of the second joint, where three are usually observed. The last olfactory rod 
is twice as long as the terminal joint of the antenna. The first pair of legs are shorter than in A. 
communis, while the head is much smaller, and of an entirely different shape. The caudal uropoda 
are dwarfed, very short, but the set® much as in A. communis. 
Remarks .—It follows from the foregoing statements that the geographical range of Gwcidotcm 
stygia is as great or greater than that of any other cave animal, unless Pseudotremia cavernarum 
be excepted. It also appears that upon the whole it does not vary much, being invariably white 
in color, blind, usually with no traces of eyes, and of a narrow, elongated shape. The parts which 
vary most are the organs of sense— i. e., the first anti second antenn®, especially the first pair. 
Its parent form is evidently one of the species described from Illinois, and as Asellus communis 
is widely distributed over the Mississippi valley and the Atlantic States, we are justified in 
regarding this as the parent form. It seems to be more abundant than any other species of the 
genus. This is evidently due to its immunity in its subterranean retreats from the attacks of 
the host of enemies—insect, crustacean, and fish—which prey upon the eyed out-of-door forms. 
Although blind, its loss of eye-sight is made up to it by its greater development of sense- 
appendages (antenn®), though after all the loss of sight is perhaps of little moment, since it is not 
exposed to the attacks of stronger animals. It breeds from April to May in Mammoth Cave, and 
probably all summer, since it was found by Mr. Hubbard with eggs in Cave City Cave, July 29, 
1881, and in wells with eggs in Illinois by Mr. Forbes. The number of eggs produced and kept 
within the incubatory pouch appears to be no greater than in the out-of-door forms. 
We think we have shown that on taxonomic grounds the genus C®cidot®a is as well founded 
as many other.genera which are accepted by carcinologists. It presents, at any rate, certain 
constant differences from the blind species of European wells and caves, as well as the dark 
abysses of Lake Geneva, and though exposed to the same general surroundings, has developed 
in different directions. It affords an interesting example of the origin of generic characters by 
changes in an environment the nature of which we can easily estimate. 
Crangonyx vitreus Smith. PL Y. figs. 1 to 4. 
Stygobromus vitreus Cope, Amer. Naturalist, vi, 422, July, 1872. 
Not Crangonyx vitreus Packard, Fifth Aim. Rep. Peab. Acad. Sci., Salem, 95, 1873. 
The following description and accompanying sketches on Plate Y have been kindly prepared 
by Prof. S. I. Smith, of Yale University: 
All the Ampliipods which I have seen from the Mammoth Cave belong to a single species, 
undoubtedly the same as the one badly described from the same locality by Professor Cope. In 
all I have examined five specimens, collected by Professor Packard in Shaler’s Brook, the Laby¬ 
rinth, and Willie’s Spring. 
The largest specimen, the one figured, is from Shaler’s Brook, and was found under a stone. 
This specimen is a female, 5.2“ m in length (from the front of the head to the tip of the telson). 
The secondary flagellum of the antennul® is minute, scarcely larger than the first segment of the 
flagellum, very slender, and composed of two segments, of which the terminal one is very minute, 
and about one-third as long as the first segment. The caudal stylets are all short and stout, the 
first and second pairs, with the outer rami, a little shorter than the inner, and both armed with 
spines which increase in length distally and at the tips are very long and slender; the third, or 
posterior pair, are almost rudimentary, being much shorter than the telson. The basal portion 
