REPORT ON THE CRUSTACEA MACRURA. 



193 



This family consists of several genera, dependent rather on their external characteristic* 

 than on their branchial arrangement, as may be seen by the following table :— 



Northern Hemisphere — 



Cambarus, 



Astaeas, . 

 Southern Hemisphere — 



Astacoides, 



Parattacus, 



Paranephrops, 



Astacopsis, 



Engxus, . 



Cherops, . 



Pleurobranchioe. Arthrobranchiie. Podobranchiw. 





 1 + 2/ 



1 

 4 

 4 

 4 

 4 

 4 



These two groups correspond with Astacus and Astacoides of most authors, and 

 with those of Dana, excepting that he eliminates Paranephrops from the latter, and 

 places it near to the marine genus N&phrops. 



With regard to the genera there is no species from the northern hemisphere in this 

 collection, and only three from the southern group, and these belong to the genus 

 Astacop>sis (Huxley). 



Geographical Distribution. — The range of this family is peculiar, the several genera 

 being adapted each to its own locality, no two genera being known to exist in one habitat. 

 Several species of Astacus have been found in many of the rivers of Europe and Asia, 

 the islands of Japan, and, according to Faxon, five species exist in rivers in North 

 America, west of the Rocky Mountains, as first noticed by Dana ; whereas on the 

 authority of the same writer fifty-two species of Cambarus inhabit most of the rivers 

 and lakes of North America east of the same range of hills. 



Geologically Cambarus has been found as early as the lower Tertiary deposits of the 

 Bear River Valley, Western Wyoming, in North America, and Astacus in the Cretaceous 

 beds of Europe, and approximating genera such as Eryma in still earlier formations. 



Development. — The young quits the ovum in the Megalopa stage, having all its 

 appendages present in a more or less perfect condition. This was shown by Rathke 1 

 in 1829, to whose account little has since been added. 



Dr. Hagen 2 says, "it is easy to discriminate between the sexes of very young 

 individuals of Cambarus clarkii. This is the case with those only 0"3 inch long, and 

 while they still occupy the postabdomen of the mother. In the females the sexual 

 aperture is visible at the base of the third set of legs. The first abdominal segment is 

 without any appearance of abdominal legs ; in all the other segments the abdominal legs are 

 well developed, their length being nearly two-thirds of the breadth of the post-abdomen, 

 the basal article being oblong, while the length of the double flagellum is a little greater." 



1 Entwickelung des Flusskrebses, 1829. 



(ZOOL. CHALL. ESP. PART LII. 188G.) 



- Monograph of the North American Astacidse, p. 142. 



Fff 25 



