126 CALIFORNIA ACADEMY OF SCIENCES. 



51. Mytilimeria nuttalli Conrad. 



Plate XVII, Fir.. 8. 



Mytilimeria fmiia/Zi Con., ] own. Phil. Acad. Sci., Vol. VII, 1837, p. 247. Cpr., Brit. Assn. Rept., 

 1863. p. 638. Gabb, Pal. Cal., Vol. II, p. 90, 1869. Tryon, Syst. Conch., Vol. II!, 

 1884, p. 147, PI. CVIII,fig. 68. Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 252. 

 Keep, West Coast Shells, p. 203, 1892. 



Shell small, equivalve, suboval, convex, thin; beaks central, subspiral, small; surface sculp- 

 tured by fine, concentric, incremental lines and numerous delicate radiating sulcations, the whole 

 having a pearly luster; hinge edentulous, with a slight linear cavity under the beaks; pallial sinus 

 broad, obtuse. 



Dimensions. — Long. 11 mm.; alt. 17 mm,; diam. 10 mm. 



This fragile little shell resembles a very small and broad MytUns, but is easily 

 distinguishable by its delicate sculpture. Specimens identified by Dr. Dall. 



Rare in the Pliocene and lower San Pedro series of Deadman Island, and in 

 the lower San Pedro series of San Pedro. 



The species figured is imperfect. It came from the lower San Pedro series at 

 Deadman Island, and is now in the collection of Delos Arnold. 



Living. — Straits of Fuca to San Diego (Cooper). 



PleiMocene. — San Pedro (Cooper; Arnold). 



Miocene. — Tomales, Marin County (Cooper). 



Superfamily POROMYACEA. 

 Family XVII. VERTICORDIIDiE. 



Genus Verticordia S. Wood. 



Shell suborbicular, with radiating ribs; beaks subspiral; margins denticulated; interior 

 brilliantly pearly; hinge with one prominent cardinal tooth in each valve; adductor scars two, faint; 

 pallial line simple; ligament internal, oblique; epidermis dark brown. 



Type, Verticordia cardiiformis Wood. 



52. Verticordia novemcostata Adam..'^ ct- Reeve. 

 Plate XVII, Fic. 10. 



Verticordia novemcostata An. & RvR.= V. ornata D'Orb. (yfa'^CPR., Brit. Assn. Rept., 1863, p. 645.) 



Shell small, suborbicular, compressed, thin; beaks subcentral, subspiral, small, sharp, 

 anterior extremity evenly rounded; posterior dorsal margin evenly arcuate, and joining arcuate 

 ventral margin in an angular extremity; surface with nine prominent, sharp, arcuate, radiating ridges; 

 the first and third interspaces wider than the others; margins sharply denticulate; hinge with one 

 prominent cardinal tooth in each valve; adductor scars two, faint; pallial line simple; ligament 

 internal, oblique; interior pearly. 



Dimensions. — Long. 4 mm.; alt. 3.5 mm.; diam. 2 mm. 



