40 
MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 
This species was also found by Mr. J. B. Proctor to occur id Bat Cave, Edmonson county, 
Kentucky, June 13,1874. It does not differ from Mammoth Gave examples. The larger hand is 
on the left side. One female collected by Mr. Sanborn in a cave near Haunted Cave, same county 
and State, was rather small, but presented no differences from Mammoth Cave females. 
In none of the specimens examined did the rudimentary eyes seem to vary. 
Relation of 0. pellucidus to out-of door species of Gambarus. —In comparing pellucidus with 0. 
bartonii , a young male of Form II, 1.30 inches long, from Mammoth Cave, it was found to differ from 
C. bartonii in the spinnles on each side of the apex of the rostrum. 
It seems to us that 0. pellucidus is, in the proportions of the body and particularly the shape 
of the rostrum more like 0. bartonii thau G. affinis. G. pellucidus differs from C. bartonii in the 
longer baud and the fourth joint of the limb, while the thorax and rostrum are much longer. The 
antenna; are rather the stouter and shorter in G. pellucidus. The elongated body, long hands, 
and the limbs bearing them are changes such as we would expect to meet with in cave animals. 
The G. bartonii, which is a good deal bleached, is as white and as pale as the pellucidus, except 
that the head and first pair of limbs and hands have scattered blackish speckles. 0 . affinis is 
evidently, however, the parent form of G. pellucidus. On comparing males of Form II of the two 
species, G.pellucidus has stouter and larger second antennge; the antennal scale is broader at the 
end, the rostrum is wider, the head is rather'wider and shorter, the hinder edge is less convex, the 
thorax is a third longer, the abdomen but slightly longer, the difference being in the cephalo- 
thorax. The ischium of first pair of legs is one-third as thick and about one-third as long, the 
meros one-half as thick and one-third longer; the carpus is of about the same length, but the 
hand is one-half as wide and a little longer thau in G. affinis. Of the four succeeding pairs of feet 
the ischia are about the same length, the meros somewhat longer. The first antennae are longer 
and slenderer. 
The gonopods in Form II are very distinct from the out-of-door species, being nearly one-hall 
shorter. 
Gambarus rusticus, which is closely related to G. affinis, was found by us in abundance at a 
point only about 20 feet from the mouth of the cave in the brooks which flow out of Bradford 
Cave; inside of the cave pellucidus is not uucommou. 
Remarks. —Two alternatives present themselves in considering the origin of the form pellu¬ 
cidus. First, it either is derived, with G. affinis, from a common ancester; or second, and what 
seems more probable, it is a modification of G. affinis or an allied species, e. g., rusticus. The 
characteristics which separate G. pellucidus from G. affinis or G. bartonii or any out-of-door species 
are those which have been induced by its life in total darkness and the diminution in its food- 
supply. The close neighborhood of the habitat of the two forms at the Bradford Cave, the blind 
one living only a few yards away and in the upper part of the same brook as G. rusticus , is very 
significant, and this affords us the best means of ascertaining the origin of this form. It is paral¬ 
leled by the probable origin of the Myriopod Scoterpes from Trichopetalum and of Pseudotremia 
from Lysiopetalum. 
Cambarus iiamttlatus (Cope and Packard). 
Orconectes hamulatus Cope and Packard, Amer. Naturalist, xy, 881, PI. vii, figs. 1, la, 1 b, Nov., 1881. 
Cambarus hamulatus Faxon, Proc. Amer. Acad. Arts and Sci., xx, 145, 1884; Revision of the Astacidse, Mem. 
Mus. Comp. Zool., x, 4, 81. PI. iv, fig. 6, ix, figs, la, la', Aug., 1885. 
In this species the epistoma is much as that of G. bartonii, but shorter and broader; while the 
median terminal tooth is less marked than in G. latimanus, and the sides fall away rapidly from 
the front margin. It is entirely different in shape from that of 0. pellucidus. The antennal lamina 
is shorter, broader, and much more rounded on the inner edge than in G. pellucidus, and in this re¬ 
spect differs from G. latimanus. The rostrum is narrower than in 0. pellucidus, while the first pair 
of (large) claws are much slenderer, and the telson narrower than in C. pellucidus. The most ob¬ 
vious difference is seen in the modified first and second pairs of abdominal feet of the male, to 
which we may apply the term gonopod, for it is not properly an intromittent organ.* The first 
and second pair of gonopods differ decidedly from those of G. pellucidus, and closely resemble 
those of Form II of Gambarus latimanus (from Athens, Georgia, figured by Hagen), those of the 
