262 CALLISTOCHITON. 



a. Central areas having a pitted or net-like pattern toward the- 

 beaks. 



b. Mucro posterior, not depressed, tail valve with 7 ribs;, 



scales smooth, pulchellus. 



bb. Mucro subcentral, the slope behind it concave, scales 



striated, shuttleworthianus. 



bbb. Mucro subcentral, tail valve rapidly sloping backward" 



from the front margin ; eaves narrow ; scales striated, 



antiquus. 



aa. Central areas smooth in the middle, decoratus.. 



aaa. Central areas sculptured throughout with parallel lirse. 



b. Posterior area of tail valve swollen above the anterior 

 area, palmulatus. 



bb. Posterior area not higher. 



G. Mucro posterior ; riblets converging on ridge, 



crassieostaius.. 



cc. Mucro subcentral, riblets not converging on ridge.. 

 d. Profile of tail valve convex, mucro obtuse, 



infortunatus.- 



dd. Profile of tail valve rapidly sloping back- 

 ward from the front margin, mucro flat, 



gabbi. 



The species elenensis and expressus from western Middle Amer- 

 ica, and adenensis from the Red Sea, probably belong in the last 

 section of the above table, but I have seen no specimens. C.jacob- 

 ceus of Gould also belongs near infortunatus, probably. 



C. PALMULATUS Carpenter, n. sp. PI. 58, figs. 7-16. 



Shell similar to C. pulchellus, but more flattened, the dorsal ridge 

 acute; mucro subcentral, depressed, the posterior area strongly 

 swollen; sculpture stronger; central areas having about 10 sub- 

 parallel acute lirse on each side, pectinating the sutures, interstices 

 deeply cancellated; lateral areas having two strong ribs bearing 

 strong tubercles, the sutures dentate, interstices deeply punctate. 

 Anterior valve having 11 ribs, of which the outer two are joined; 

 posterior valve 7 very strong ribs bifurcating behind. 



Interior : anterior valve having 11 slits, central 1 slit, the teeth 

 normal ; posterior valve having 26 slits, the teeth crowded, minute, 

 palmate. Eaves very strong; sinus small, strongly laminate, the 



