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 C. latimanus, but the joint is much more acute than in C. 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 aud 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 C. hamulatus is quite unlike the latimanus 

 form of C. obesus, the scale of the second antennae being very different, the chelae one-half as 



wide, aud the antennae much longer, while the rostrum is much longer aud more pointed. 

 of the largest male, 5 centimeters. 



Cambarus hamulatus is quite different from C. pellucidus of 

 Mammoth aud Wyandotte caves in the rostrum, the slender 

 hands, the much broader antenna! scale, and in the form of the 

 gonopods, while the whole creature is slightly slenderer than C. 

 pellucidus, though the rudimentaiy eyes are of the same propor- 

 tion to the neighboring parts as in the other species. 



It is obvious that the form from which C. hanmlatus has 

 been derived is quite different from that which has given origin 

 to the blind crayfish of the Kentucky and Indiana caves. The 

 most common species in Northern Georgi&is Cambaruslatimanus, 

 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 Cambarus latimanus that 

 we look for the ancestors of Cambarus hamulatus. On the other 

 hand, in the form of the body, of the scale and rostrum, as well 

 as of the upper lip and thechehe (though not of the gonopods), 

 C. hamulatus approaches Cambarus 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 au examina- 

 tion of several types and the excellent figures of Dr. Hagen, 

 that C. 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 Nick ajack blind cra\fish 

 ruay have been an immediate derivative of C. latimanus of the 

 Gulf States, it probably .ultimately originated from C. affinis, 

 a more wide spread species. 



Prof. W. Faxon, in his " Revision of the Astacidse," remarks 

 as follows regarding this species, based on au examination of 

 four males, Form II, aud two females, the types of Cope and 

 Packard's description : 



In general form aud 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. oartonii group. Tho rostrum tapers towards the tip 

 more than it does in the typical form of C. pellucidus, resembliug, in this 

 respect, the form C. pellucidus iiicrmis. The terminal segment of the telson 

 narrows at the hinder end more than in C. pellucidus. I do not find the 

 differences in the mandibles, antennal scales, aud chelae mentioned by 

 Packard. 



Leugth 



Fir,. 10. — Cambarus hamulatum a, antennal 

 scale; b, gonopodof the iirst pair; all-enlarged. 

 (Kingsli y, del.) 



*Xote on the function of the gonopods.— As stated by Milne Edwards and others, the gonopods of the crawfish 

 are not iutromitteut, but 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 orgaus of the Crustacea, since they are 

 only modified limbs. 



