62 BULLETIN 97, UNITED STATES NATIONAL MUSEUM. 



A 1 . Dactyls of first 3 ambulatory legs bifurcate. Palate without longitudinal 

 ridges. Carapace subpeiitagonal Dissodactylus, p. 114. 



Genus PINNOTHERES Latreille. 



Pinnotheres LATREIT,LE, Hist. Nat. Crust., vol. 3, an X [1801-2], p. 25; type, 



7'. jnsum (Linnaeus). 



Pinnotltcra DANA, U. S. Expl. Exped., vol. 13, Crust., pt. 1, 1852. p. 380. 

 Cryptophrys RATHBUN, Proc. U. S. Nat. Mus., vol. 1G, 1893, p. 250; type, C. 



conchnrum Ratbbun. 

 Arcothcres NATJCK, in Biirger, Zool. Jahrb., Syst., vol. 8, 1895, p. 361 ; type, 



A. palacnsis BUrger. 



Zaops RATHBUN, Araer. Nat., vol. 34, 1900, p. 588; type, Z. dcprcssa (Say). 

 Pinnotcrcs ALCOCK, Journ. Asiat. Soc. Bengal, vol. C9, 1900, p. 337. 



Females larger than males. Young females similar to males. 



Carapace usually ill calcified in female, often calcified in male, 

 generally convex with ill-defined edges; in shape transversely oval 

 or circular or subquadrangular to suboctagonal, with rounded an- 

 gles, sometimes longer than wide; generally surface smooth and 

 regions not defined, occasionally surface uneven and regions indi- 

 cated. 



Front narrow, generally deflexed in female, more often advanced 

 in male. Orbits small in female, larger in male, circular or oval; 

 eyestalks short. Antennules oblique. Antennas small, the minute 

 flagellum standing in inner angle of orbit. 



Epistome well defined. Buccal cavity crescentic, arched and very 

 broad from side to side, but very short fore and aft. The external 

 maxillipeds completely close the cavity; they consist chiefly of the 

 merus which is fused with the ischium to form ;i single large ob- 

 liquely-directed joint carrying the flagellum at its inner end; palpus 

 typically small, though sometimes large, even half as large as the 

 merus ; it consists usually of three segments, the dactylus most often 

 inserted on the inner or flexor border of the propodite but sometimes 

 attached to the distal end of the propodite; very exceptionally the 

 palpus consists of only two segments, the dactylus being absent; 

 exognath for the most part concealed. 



Chelipeds short, equal, and generally stouter than legs; legs of 

 moderate length. Abdomen consisting usually of seven separate 

 segments ; in male narrow, in female often larger than the sternum. 



Habitat. Commensal in lamellibranch and sometimes in gastero- 

 pod mollusks, in tunicates, annelids, and sea-urchins. Males usually 

 free-swimming. 



Range. Widely distributed in the shallow waters of tropical and 

 warm-temperate seas. 



Remarks. Several species formerly placed in other genera are 

 now ranged in Pinnotheres. Ostracotheres politus is found to have 

 three segments to the palp of the outer maxilliped instead of two, 



