Ortmann : A New Cambarus. 416 



Altogether there are thirteen males of the first form, eight males of the 

 second form, and nine females. 



The specimens were collected on May 25, 1910, by Dr. D. A. 

 Atkinson of Pittsburgh, and the specific name is given in honor of the 

 discoverer. 



Remarks. — This species is morphologically and geographically 

 interesting. It stands closest to C. cubensis Erichson, but differs 

 principally in the much less dilated inner face of the copulatory organ. 

 In the latter respect it comes nearer to the continental forms, 

 C. williamsoni Ortmann and C. pilosimanus Ortmann from Guate- 

 mala, and C. mexicanus Erichson from Mexico. But it has not the 

 copulatory organs of these species, the chief difference being discov- 

 ered in the long setiform tip of the inner part, which is also found in 

 C. cubensis. 



C. williamsoni, pilosimanus, and mexicanus resemble each other in 

 the copulatory organs, but C. mexicanus is more remote from the 

 others (and also from C. atkinsoni and cubensis) because of the absence 

 of spines on the margins of the rostrum and the sides of the carapace. 

 C. williamsoni and pilosimanus have two spines on each side of the 

 carapace, and their areola is much narrower than in C. atkinsoni, 

 and also narrower than in C. cubensis. In C. atkinsoni the areola 

 is distinctly wider and shorter than in C. cubensis, and in this char- 

 acter, and in the more concave surface of the rostrum, and the slightly 

 longer acumen of the latter, aside from the differences in the shape of 

 the copulatory organs, C. atkinsoni differs from C. cubensis. C. 

 cubensis also has the spines on the sides of the carapace often rudi- 

 mentary or absent. 1 



C. atkinsoni forms in the copulatory organs a connection between 

 the Cuban forms and those of the mainland, which is interesting, be- 

 cause the geographical range is also intermediate. But the copu- 

 latory organs of C. atkinsoni distinctly indicate the cubensis-type in 

 its beginning. In the shape of the rostrum, its marginal spines, and 

 in the lateral spines of the carapace, C. atkinsoni is rather indifferent; 

 in the shape of the areola it is distinctly more primitive than any of 

 the species allied with it. The Guatemalan forms are in this respect 

 even more advanced than C. cubensis, while both C. atkinsoni and 

 cubensis are more highly specialized in the copulatory organs than the 

 Guatemalan forms. 



1 See Faxon, in Bull. Mus. Comp. Zool., LIV, 1912, pp. 458-459. 



