MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 
41 
first pair being shorter, thicker, and the last joint being much bent, hook or sickle-shaped, 
whence the specific name hamulatus. The first gonopods differ in the proportion of parts from 
those of G. latimanus, but the joint is much more acute than in G. latimanus. 
The first pair of gonopods, compared with the latimanus form of obesus from Maryland, given 
me by Mr. Uhler, are much like it in general form, but the sinuous branch is longer and straighter, 
while the hook is much slenderer. In the second pair of accessory gonopods the knob is propor¬ 
tionately smaller. In other more important characters G. liamulatus is quite unlike the latimanus 
form of G. obesus , the scale of the second antennae being very different, tbe cliche one-half as 
wide, and the antennae much longer, while the rostrum is much longer and more pointed. Length 
of the largest male, 5 centimeters. 
Gambarus hamulatus is quite different from C.pellucidus of 
Mammoth and Wyandotte caves in the rostrum, the slender 
hands, the much broader antennal scale, and in the form of the 
gonopods, while the whole creature is slightly slenderer than <7. 
pellucidus, though the rudimentary eyes are of the same propor¬ 
tion to the neighboring parts as in the other species. 
It is obvious that the form from which G. hamulatus has 
been derived is quite different from that which has given origin 
to the blind crayfish of the Kentucky and Indiana caves. The 
m ost common species in Northern Georgia is Gambarus latimanus, 
which has been found at Athens and Milledgeville, Georgia, and 
probably is abundant in the northern limestone region of Ala¬ 
bama. At any rate, it is perhaps to Gambarus latimanus that 
we look for the ancestors of Gambarus hamulatus. On the other 
hand, in the form of the body, of the scale and rostrum, as well 
as of the upper lip and the chelae (though not of the gonopods), 
G. hamulatus approaches Gambarus affinis. Now, of all our 
North American crayfishes, it would appear, as Mr. Uhler has 
told the writer, and as seems evident to us upon an examina¬ 
tion of several types and the excellent figures of Dr. Hagen, 
that G. affinis is the more generalized form, and this is tanta¬ 
mount to saying that it is the ancestral form of our North 
American crayfishes. So, while our Nickajack blind crayfish 
may have been an immediate derivative of G. latimanus of the 
Gulf States, it probably ultimately originated from 0. affinis-, 
a more wide-spread species. 
Prof. W. Faxon, in his “ Revision of the Astacidae,” remarks 
as follows regarding this species, based on an examination of 
four males, Form II, and two females, the types of Cope and 
Packard’s description: 
In general form and appearance it bears a close resemblance to C. 
pellucidus, but the carapace is less spiny, and the male has hooks on the third 
pair of legs only, and the first pair of abdominal appendages are formed after 
the fashion of the C. hartonii group. The rostrum tapers towards the tip 
more than it does in the typical form of C. pellucidus, resembling, in this 
respect, the form C. pellucidus inermis. The terminal segmeut of the telson 
narrows at the hinder end more than in G. pellucidus. Ido not find the Fig. 10. — Gambarus hamulatus: a. antennal 
differences in the mandibles, antennal scales, and chelse mentioned by se^lw^ gonopodottheJistpair, all enlarged. 
Packard. 
* Aote on the function of the gonopods. —As stated by Milne Edwards and others, the gonopods of the crawfish 
are not iutroiuittent, hut simply rude gutters for the passage of the fertilizing fluid to the eggs. It is obvious that in 
the lobster the gonopods form simply a rude tube or gutter to conduct the seminal fluid to the eggs as they pass back¬ 
ward from the oviducts to the swimming feet of the female. During the process of fertilization of the eggs the male, 
without doubt, as in the crawfish, holds the female by the claws, she resting on her back. The term gonopod is ap¬ 
plied for convenience in descriptive carcinology to the external reproductive organs of the Crustacea, since they are 
only modified limbs. 
