MOPALIA. 303 



M. SINUATA Carpenter. PL 62, figs. 95, 96, 97. 



Shell oblong, elevated and strongly carinated, the side-slopes, 

 straight. Color whitish, clouded with delicate blue-green and macu- 

 lated with rich tawny brown. 



Median valves hardly beaked, the lateral areas not raised, but 

 strongly defined by an elevated diagonal rib ; sculptured with two 

 oblique series of fine riblets forming a latticed pattern. Central 

 areas having a series of longitudinal curved riblets converging 

 toward the median keel, crossed by curved radiating threads a 

 little finer and less prominent (fig. 97). Anterior valve having 8 

 (not counting the posterior sutural borders) strong radiating ribs 

 narrower than the latticed intervals. Posterior valve depressed, the 

 mucro being at the posterior third. 



Interior bluish-white. Sinus very small and narrow. Anterior 

 valve having 8 slits, median 1 slit ; teeth thickened outside at the 

 edges of the slits. Posterior valve (fig. 96) having a deep rounded 

 median sinus behind (which is continued upward in a superficial 

 excavation to the mucro), and a single slit on each side. 



Girdle rather narrow, leathery, " dusty " bearing a few hairs, with 

 .a rounded pore at each suture (fig. 95). 



Length 11 J, breadth 7 mill.; divergence 105. 



Puget Sound (Kennerley) ; San Francisco Bay (Newcomb). 



f Mopalia sinuata CPU., Proc. Acad. Nat. Sci. Phila., 1865, p. 59. 

 Placiphorella sinuata CPU., MS. and in DALL, Proc. U. S. Nat. 

 Mus. 1878, p. 303, 3Q6. Osteochiton sinuatus BALL, I.e. 1886, p. 

 211. 



This little species has the form and sculpture of the true Mopalias, 

 but it differs from them in the posssesion of a bristle or hair-bearing 

 pore at each of the sutures, the girdle elsewhere bearing sparsely 

 scattered hairs on the leathery, minutely roughened surface. It 

 resembles M. imporcata but is sufficiently different in sculpture. 



My description and figures are from Carpenter's type specimen, 

 now in the Smithsonian collection. 



M. CILIATA Sowerby. PL 64, figs. 64-73. 



Shell oblong, rather depressed, the dorsal ridge carinated (some- 

 times rounded), side-slopes straight or somewhat convex. Surface 

 lusterless, finely sculptured, variously colored, usually either (1, 

 typical coloring) verdigris green maculated with black or black- 

 brown, the girdle yellow (fig. 65) or (2) maculated with maroon 

 and sometimes touched with rich chestnut on the ridge, or having 



