128 A REVISION OF THE ASTACID^. 



barely indicated as a minute tubercle. In A. Dauricus tbe post-orbital 

 spine is more prominent ; it lies very close to the margin of the cara- 

 pace ; the ridge continues but a \e.\-y short distance backward from the 

 spine. In A. Schrcnckii 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 bcliind the cervical suture. Rostrum concave and lightly carinate above. 



a. Rostrum equal iu length to peduncle of antennaj. Abdominal pleura narrow, pointed. A. Daurirns. 



b. Rostrum shorter than peduncle of antennae. Abdominal pleura broad, rounded. . . A. Juponicus. 



1. Astacus (Cambaroides) Japonicus. 



Plate X. figs. 10. 10' (first abdominal appendages of male). 



Astacus Japonicus, De Haan, Crustacea of Siebold's Fauna Japonica, p. 164, Tab. XXXV. fig. 9, 1S42. 

 Astacus Japonicus, Ericiison, Arch. Naturgesch., XII. Jalirg., I. O-i, 1846. (After De Haan.) 

 Astacus Japonicus ? Kessler, Bull. Soo. Imper. Nat. Moseou, XLVIII. 3G4, 1S74. 

 Astacus {Cambaroides) Japonicus, Faxon, Proc. Amer. Acad. Arts and Sci., XX. 149, 1884. 



Habitat. — Japan. 



Prof C. 0. Whitman, to whom the Museum of Comparative Zoology 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 

 i-sland 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. Gamhelii, 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; — 



