436 Annals of the Carnecie Museum. 



An attempt has been made, in the paper referred to, to also inchide 

 these forms in Cambarus, but, as is now evident, this is im])Ossible. 

 The material at hand when the pa])er was written was too poor (only 

 one male of the second form of C. (/i<ii(cti) to decide the question, 

 and, moreover, the description of these organs in C. viexicamis was 

 not well understood, since no figure had been published. 



However, Faxon's description of the male organs of C. 7iiexicaniis 

 suddenly became clear to me when I compared it with the new species, 

 and plainly these organs in these two species are very similar. Since 

 good figures of those of the other two species have been published, it 

 is now possible to give a correct account of these organs, and to point 

 out their chief peculiarities. 



Faxon's description of the male copulatory organs in his first and 

 second group is as follows: '■^ Outer part truncate at the tip, and fur- 

 nished ivith one to three small recurved teeth ; inner part terminated by 

 a short acute spine, ivhich is generally directed outward. 



For the subgenus Cambarus, I have given the following characters 

 of the male organs : ' ' Sexual organs of male stout, more or less straight, 

 and co)nparatively short, truncated or blunt at the tip, the outer part 

 ending in one to three horny teeth, which are sometimes recurved, or 

 compressed, or plate-like, and are always sharply distinguishable by means 

 if the blunt end. Inner part terminated by a shorter or longer acute 

 spine, which is sometimes distinct from the tip of this part, so that it 

 appears twofoi/itcd. ' ' 



This latter description was framed with the desire to make it fit the 

 species of the digueti-grou]) ; but it neglects the fact, that in these 

 species the outer part of the male organs does not possess any horny 

 teeth, as is generally the case in species of the type of blandingi. In 

 the species of the digueti-gxon^^, it is the inner part that possesses, in 

 the male of the first form, a single horny spine, which has a variable 

 position in the different species, but is always highly characteristic for 

 one and the same species. It has taken me some time to ascertain 

 this fact ; indeed, I admit that I may be mistaken in so far as that 

 there is a remote possibility that this horny spine belongs to the outer 

 part, since in the new species to be described here, its position is just 

 at the point where the two parts (inner and outer) become distinguish- 

 able at the anterior margin of the organ ; but after examining the con- 

 dition in second form males of the new species and of C. digueti, I feel 

 rather sure that this accessory tip, which is not horny and spiniform 



