191 



The length of the carapace and rostrum, measured in the middle line, is 21 

 millim., of the abdomen 33 millim. 



From the Bay of Bengal, off Ceylon, 54-2 fathoms. 

 Regd. No. — (Type of the species). 



Subgenus Calastacus, Faxon. 



Calastacus, Faxon, Bull. Mas. Comp. Zool. XXIV. 1893, p. 194, and Mem. Mus. Comp. Zool. XVII I. 1895. 

 p. 105. 



Calastacus agrees with Calocaris in every respect except that the " scapho- 

 cerite " and " stylocerite " of the antennal peduncle are conspicuous spines, as 

 they are in Iconaxiopsis. 



According to Faxon, the somite (VIII) which carries the 2nd maxillipeds 

 has neither podobranch nor arthrobranch, but in the two Indian species which, 

 on account of their long " scaphocerite " and " stylocerite " must be assigned to 

 Calastacus rather than to Calocaris, this somite has, in addition to an epipodite, 

 two tapering plates with one edge distantly and minutely plumose, which un- 

 doubtedly are rudimentary podobranch and arthrobranch. 



Key to the Indian species of Calastacus. 



I. Some lank silky setce on the carapace and abdomen : on the gastric 

 region, behind the spines at the base of the rostrum, is a horse- 

 shoe of spines ... ... ... ... ... G. felix. 



II. No long setce on the carapace or abdomen: no spines behind those 



at the base of the rostrum ... ... ... ... G. investigatoris. 



ill. Calocaris {Calastacus) investigatoris, Anderson. 



Calastacus investigatoris, Anderson, Journ. Asiatic Soc. Bengal, LXV. pt. 2, 1896, p. 97. 

 Illustrations of the Zoology of the Investigator, Crustacea, Plate XXV. Fig. 1. 



Carapace (rostrum included), measured in the middle line, as long as the 

 first 5- abdominal somites, studded with sharpish vesiculous granules, finely 

 carinated in the middle line, the carina terminating in a vesiculous tubercle and 

 having a similar tubercle in the middle of its gastric course : the cervical and 

 branchial grooves very conspicuous. 



The rostrum does not quite reach the end of the 2nd joint of the anten- 

 nular peduncle : its sides are prolonged on to the gastric region as two sharp 

 ridges, each of which carries two spines. 



The abdominal pleura behind the subacute 1st, are broadly rounded and 

 have the surface somewhat corrugated : they decrease in length from the 2nd 

 to the 5th. Telson broadly rounded off, as long as the caudal swimmerets, 



