CALLISTOPLAX. 289 



dinal lirulae ; central areas with about 10 rugulose-granose lirse on 

 each side, perpendicular to the diagonal line, the interstices cancel- 

 lated. Lateral areas having two very strong rounded ribs, the 

 front one stronger, separated by a narrow sulcus, and concentrically 

 wrinkle-granose and very minutely granulose ; sutures with a series 

 of imbricating granules. Anterior valve having 7 ribs, of 

 which the posterior ones (as in the median valves), bifurcate, and are 

 imbricated along the sutures ; posterior valve in the young shell 

 having 6 ribs, all of these bifurcate, and the anterior ones split 

 twice, making 14 delicate, flattened ribs, which tend forward some- 

 what. 



Interior : the posterior valve, in a young specimen has about 11 

 slits, the teeth curved in harmony with the external ribs, and 

 directed radially outward ; in the adult there are about 12 slits, the 

 teeth solid, directed somewhat forward, rugose- costate at the mar- 

 gins, concave in the middle, the eaves very heavily callous. Ante- 

 rior valve having 7-8 slits, situated in the middle of the ribs, the 

 teeth following the curvature of the outer margin, acute. Central 

 valves with 1 slit, teeth excurved, eaves wide, pectinated, spongy. 

 Sinus narrow, deep, narrowly slit on each side of the lamina, and 

 sometimes denticulated by the external sculpture. 



Girdle narrow, smooth, thin, having 40-53 bunches of long, cor- 

 neous hairs around the margin, hardly sutural (figs. 23, 24). 



Length 14?, breadth 8 mill.; divergence 120. 



Guacomayo and Puerto Portrero (Cuming) ; China Seas (Cum- 



Chiton retusus SOWB. P. Z. 8. 1832, p. 28, Conch. Illustr. f. 22. 

 REEVE, Conch. Icon., t. 17, f. 99. Plaxiphora retusa H. & A. Ad. 

 Genera Rec. Moll, i, p. 481. Callistoplax retusa CPU. MS. and in 

 Dall, Proc. U. S. Nat. Mus. 1881, p. 286. 



The locality " China Seas " given by Cuming to Carpenter, is 

 probably wrong, that originally given by Sowerby being much more 

 worthy of confidence. The above description is from Carpenter's 

 MS. 



Figures 17-23 represent a young specimen ; in the adult the ribs 

 become more numerous and the tail-plate more " Acanthoid " in 

 appearance (figs. 25, 26). 



19 



