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, palmiilatus.. 



bb. Posterior area not higher. 



c. Mucro posterior ; riblets converging on ridge, 



crassicostalus* 



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. PL 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 



