THE SPIDER CRABS OF AMERICA 507 



similar shape, are shoved up into greater prominence and theii* sur- 

 faces smoothed off. 



Range. — Lower part of Gulf of California; Galapagos Islands. 

 Shallow water to 10 fathoms. 



Material examined. — See table, page 503. 



Genus TYCHE Bell 



« 



Tyche Bell, Proc. Zool. Soc. London, vol. 3, 1835 (1836), p. 172; type, T. 



lamellifrons Bell; Trans. Zool. Soc. London, vol. 2, 1836, p. 57. — A. Milne 



Edwards, Crust. R6g. Mex., 1878, p. 125. 

 Glischirus Gistel, Natur. Thierreichs., 1848, p. XI; substituted for Tyche 



Bell, supposed to be preoccupied by Tychus Leach, 1817. 

 PlaUjrinchus Desbonne, in Desbonne and Schramm, Crust. Guadeloupe, 



1867, p. 3; type, P. trituberculatus Desbonne. 



Carapace oblong-oval, flattened, with lamellate expansions in front 

 and behind ; front very wide, with four horns, the two lateral forming 

 anterior angles of orbit. Orbits covered by a lamellate prolongation 

 which conceals the ocular peduncles nearly to their extremities; 

 below there is no orbital floor, and the ocular peduncles are entirely 

 uncovered. Antennae concealed beneath rostrum; basal segment 

 somewhat enlarged, a small blunt point at its antero-external angle; 

 following articles cylindrical. The external maxillipeds exhibit a 

 very remarkable arrangement, not shown in any other genus: The 

 external branch or exognath is narrow and has at its base a falci- 

 form prolongation which is bent around forward and lodged in a 

 groove of the ischium of the endognath. The merus is much extended 

 backward and then inward so as to cut deeply the anterior border of 

 the ischium. 



Chelipeds little enlarged. Ambulatory legs slender, with very 

 hooked dactyli. 



Known only from the two species here described. 



KEY TO THE SPECIES OF THE GENUS TYCHE 



A^ Preorbital horns subparallel. Posterior margin of carapace not medially 

 notched lamellifrons, p. 508. 



A^. Preorbital horns strongly divergent. Posterior margin of carapace medially 

 notched emarginata, p. 508. 



Analogous species on opposite sides of the continent: emarginata 

 (Atlantic) ; lamellifrons (Pacific) , 



