SCHIZOCHITON. 235 



posterior sinus, however, is unlike the former group, in which the 

 tail valve approaches the head valve in form ; and the arrangement 

 of the eyes is the same as in Lorica, which has a degenerate tail 

 insertion-plate. At the same time, it must be granted that the differ- 

 ences between Schizochiton and Lorica are greater than between most 

 genera of the same family ; for in Schizochiton the slits of the head- 

 valve are numerically related to the external ribs; the latter bear 

 eyes, and the tail valve has a well developed slit and pectinated 

 insertion-plate. 



S. INCISUS Sowerby. PI. 51, figs. 1-8. 



Shell much elongated, narrow, the valves elevated, somewhat car- 

 inated ; surface lusterless, grayish, obscurely mottled with olive and 

 purplish. 



Median valves elongated, beaked, the lateral areas small, slightly 

 raised. Entire surface sculptured with flattened longitudinal riblets, 

 as wide as their interstices, converging toward the dorsal ridge and 

 somewhat irregular or wavy on the lateral areas ; each riblet where it 

 passes over the diagonal, enlarged for the insertion of an eye. Ante- 

 rior valve (figs. 2, 4) having 6 (sometimes 7 or 8) radiating curved 

 ribs, each bearing a series of eyes, the intervals sculptured with close 

 v-shaped riblets. Posterior valve (figs. 6, 7, 8) having the mucro 

 posterior, the latero-posterior areas tricostate, otherwise sculptured 

 like -the median valves ; posteriorly it has a wide, deep fissure, extend- 

 ing up to the mucro (fig. 8.) 



Interior whitish, stained with purple-brown in the middle of each 

 valve. Sutural plates well developed. Sinus V-shaped. Anterior 

 valve having 6, central valves 1 or 2 slits ; posterior valve, on each 

 side of the posterior fissure, 3 slits ; teeth thin, distinctly cren- 

 ulated outside. 



Girdle broad, alternately buff and dark colored, the light stripes 

 wider, and as usual, sutural ; rather thinly but in places densely 

 clothed with minute, cylindrical, shelly spinules, part brown, part 

 white. Length 50, breadth 18 mill. 



Zebu, (Cuming), and Samboangan, (Challenger), Philippines ; 

 Raines Island, Torres Straits (Ince) ; Clairmont and Bird Is., 

 N. E. Australia (Coppinger) ; Sulu Sea (Capt. Chimmo.) 



Chiton incisus SOWB., P. Z. S. 1841, p. 61. REEVE, Conch. Icon, 

 f. 43. Schizochiton incisus GRAY, P. Z. S. 1847, p. 169. SHUTTL., 

 Bern. Mittheil. 1853, p. 68. H. & A. AD., Gen. Rec. Moll, i, p. 477, 



