90 astacilu:. 



Concerning the further division of the genus Astacus into groups, I 

 am not able to give a final judgment, being entirely ignorant of the 

 Australian species, and having before me of the Amur species but one 

 female, and of the European species only Astacus flwmatiUs. 



The European species, or more precisely Astacus fluviatilis, differ from 

 all the others in having the apical part of the intermediate lamina of 

 the postabdomen separated from the basal half, although not so strongly 

 as in Cambarus ; in the American and Asiatic species this part is only 

 more or less separated at each side, it is most so in A. TrowbridgU. 



A.jkuriati&8 has a basal tooth on the exterior margin of the antennal 

 lamina, which is never to be found in any other species. This appar- 

 ently very striking character is never mentioned for A. fluviatiUs. 



The Asiatic species, A. Dauricus, differs in having a rostrum similar 

 to that of C. Bartomi, the front border of the cephalothorax strongly 

 angulated, a narrower and more elongated thorax, with a nearly straight^ 

 transverse suture and the above-mentioned form of the annulus ventralis. 



The American species are divided according to the following char- 

 acters : — 



I. Margins of the rostrum denticulated; front border of the cephalo- 

 thorax slightly angulated. 



1. Rostrum not notched in front of the tip ; cretre visible ; hands 

 barbated: A. Gambelii. 



2. Rostrum strongly notched before the tip; no cretae, but two spines 

 on each side; hands without beard: A, rdgrescens, 



II. Margins of the rostrum not denticulated ; front border of the 

 cephalothorax straight. 



1. Rostrum long, margins parallel, strongly notched hi front of the 

 tip : A. Trowbridffii. 



2. Rostrum short, tapering, slightly notched before the tip : A. Kla- 

 mathensis. 



I have not seen A. leruusculus, which differs from both the preceding 

 species in the acute angles of the segments of the postabdomen. 



My knowledge is too limited and fragmentary to authorize my say- 

 ing more respecting the geographical distribution of the species. 



1. Astacus Gambelii Girard. 



Camharus Gambelii Gir., Proc. Acad. X. S. Philad., T. G, p. 90 : p. 375 : p. 380. — Stimpson. Proc. 

 Boston Soc. X. II., T. (J, p. S7 (separat. p. 5"2). 



Figures on Fl. I., III., and XI. 

 First abdominal leg of the male: 



first form, fig. 1'7 in front ; fig. 98 outside. 

 Antennal lamina, fiir. 170, a: epistoma, b: spine of the second joint of the exterior antenna, c. 



PI. XI. Male type from California. 



Mas. Pallidus obesus, rostro modico triangular^ subplano, medio 



