CALASTACUS. 105 



CALASTACUS Fax. 

 Bull. Mus. Comp. Zool., XXIV. 194, 1893. 



Cephalo-thorax laterally compressed. Abdomen long, enlarged in the 

 middle, narrowed at each extremity, pleurte broad and rounded. Rostrum 

 long, pointed ; eyes rudimentary, subglobose, without pigment and un- 

 faceted. Second antennoe on a horizontal line with the first antennae ; the 

 second segment is armed with a long external spine (stylocerite), and a still 

 longer articulated style-shaped scale (scaphocerite). Third maxillipeds pedi- 

 form. First and second pairs of legs chelate. First abdominal appendages 

 of the male modified to serve as sexual organs (gonopods). Outer branch 

 of the swimmerets divided near the posterior margin by a diagonal suture. 

 Telson long, quadrangular. Gills composed of a central stem, bearing two 

 rows of filaments. The number and arrangement of the gills are shown by 

 the followinsr formula : — 



14 + (C) 



This genus is closely related to Calocaris Bell In both genera the con- 

 dition of the aborted eyes is the same; the two anterior pairs of legs alone are 

 chelate ; the first abdominal segment bears, in the male, a pair of specialized 

 sexual appendages, and the outer plate of the sixth pair of abdominal ap- 

 pendages is divided near the end by a diagonal suture. I have not seen 

 females of either genus, nor have I examined the gill arrangement of Calo- 

 caris, there being but two specimens of Calocaris macandrece in this Museum. t 



The presence of a long styloid scaphocerite appended to the peduncle of 



* The somite which bears the second pair of maxillipeds is here reckoned as the eighth. 

 t According to Ortmann (Zoolog. Jahrb., Abth. f. Syst., VI. 50, 1891) the branchial formula for Calo- 

 caris macandrece is as follows : — 



16 + (4) 



