128 A REVISION OF THE ASTACIDA. 
barely indicated as a minute tubercle. In A. Dawricus the post-orbital 
spine is more prominent; it lies very close to the margin of the cara- 
pace; the ridge continues but a very short distance backward from the 
spine. In A. Schrenckii the spine and ridge are more pronounced, but 
still small. 
The three species may-be separated by the following table : — 
A. Lateral spine behind the cervical suture. Rostrum convex above . . . . . . . . A. Schrenckii. 
B. No lateral spine behind the cervical suture. Rostrum concave and lightly carinate above. 
a. Rostrum equal in length to peduncle of antenne. Abdominal pleura narrow, pointed. 4. Dauricus. 
4. Rostrum shorter than peduncle of antenne. Abdominal pleura broad, rounded. . . 4. Japonicus. 
1. Astacus (Cambaroides) Japonicus. 
Plate X. figs. 10, 10/ (first abdominal appendages of male). 
Astacus Japonicus, Dw Haan, Crustacea of Siebold’s Fauna Japonica, p. 164, Tab. XXXV. fig. 9, 1842. 
Astacus Japonicus, Wricuson, Arch. Naturgesch., XII. Jalrg., I. 94, 1846. (After De Haan.) 
Astacus Japonicus ? Kussupr, Bull. Soc. Impér. Nat. Moscou, XLVIII. 364, 1874. 
Astacus (Cambaroides) Japonicus, Faxon, Proc. Amer. Acad. Arts and Sci., XX. 149, 1884. 
Habitat. — Japan. 
Prof. C. O. Whitman, to whom the Museum of Comparative Zodlogy is 
indebted for four specimens of this species, informs me, that, during his 
residence in Japan, he could not learn of its occurrence in Niphon, the 
main island of the Empire, all the specimens known to him coming from the 
island of Yesso. Kessler’s specimens came from the same locality as Prof. 
Whitman’s, viz. Hakodadi, Yesso. 
In the four specimens received from Prof. Whitman, the posterior mar- 
gin of the telson is rounded, and shows no trace of the deep median notch 
described and figured by De Haan. In this respect, these examples agree 
with those described by Kessler. Individuals with similarly notched telson 
are found in some other species, e. g. A. Gambelii, although in these the 
emargination is less pronounced. 
The rostrum terminates in three minute horny points. The branchial 
formula is the same as in Astacus fluviatilis, there being one pleurobranchia 
(on each side) on the last thoracic somite, and one rudimentary pleuro- 
branchia, in the shape of a simple filament, on each of the three antecedent 
somites. 
The arrangement of the gills is shown in the following table: — 
