CALASTACUS. 105 
CALASTACUS Fax. 
Bull. Mus. Comp. Zodl., XXIV. 194, 1893. 
Cephalo-thorax laterally compressed. Abdomen long, enlarged in the 
middle, narrowed at each extremity, pleure broad and rounded. Rostrum 
long, pointed; eyes rudimentary, subglobose, without pigment and un- 
faceted. Second antennz on a horizontal line with the first antenne; 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 following formula : — 
Somites vii.* exe Xs Ks XII. XM XLV 
Epipods 1 1 1 1 1 il = (6) 
Podobranchiz 0 if 1 1 1 0 ORs a4: 
Arthrobranchie 0 2 2 2 2 2 Oe—a10 
Pleurobranchize 0 0 0 0 0 0 0o= 0 
© 
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 Cal- 
- carts, there being but two specimens of Calocaris macandree 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. 
+ According to Ortmann (Zoolog. Jahrb., Abth. f. Syst., VI. 50, 1891) the branchial formula for Calo- 
caris macandre@ is as follows : — 
Somites VIII. Ix. Xe XI XII. XtIIr. XIV. 
Epipods 0 0 1 1 1 1 = (4) 
Podobranchiz 1 i 1 1 1 0 a 
Arthrobranchie 1 2 2 2 2 Q 0=11 
Pleurobranchie 0 0 0 0 0 0 0= 0 
16 + (4) 
14 
