184 CALIFOUNIA ACADEMY OF SCIENCES. 



137. Zirphaea gabbii Tryon. 



Z/rfi/iiza gadi/i Tryon, Froc. Phil. Acad. Nat. Sci., 1866, p. 144, PI. I, fig. i. Gabb, Pal. Cal., 

 Vol. II, pp. 52, 88, PI. XV, fig. 10, 1869. Cooper, 7th Ann. Rept. Cal. St. Min., 

 1888, p. 270. Dall, Trans. Wagner Inst. Sci., Vol. Ill, Part 4, 1898, p. 818. 



Zirpheca crispata (non Linn., Syst. Nat., Ed. X, p. 670, 1859) {fide Dall). Cpr., Brit. Assn. 

 Rept., 1863, p. 637. Keep, West Coast Shells, p. 210, fig. 179,1892. Williamson, 

 Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 182. 



Shell of medium size, oblong, convex, thin; surface sculptured by concentric laminations, 

 which are much more elevated, and are provided with sharp, rasp-like teeth on the anterior half of 

 the shell; a slightly raised ridge, flanked by two shallow depressions, runs obliquely posteriorly from 

 the umbo, dividing the spiny sculptured area from the concentrically ridged area; valve reflexed from 

 the umbones forward, covering the umbones; each valve is provided with a delicate spoon-shaped 

 tooth or process, which joins the shell just beneath the umbo. 



Dimensions. — Long. 72 mm.; alt. 35 mm.; diani. 30 mm. 



This species, though closely allied to Z. crispata, is pronounced a distinct species 

 by Dr. Dall. Specimens identified by Dr. Dall. 



Quite rare in the upper San Pedro series at Sau Pedro, Los Cerritos, Craw- 

 fish George's, and Deadman Island. 



Pleistocene. — Santa Barbara (Cooper): San Pedro (Cooper; Arnold). 



Miocene. — (?) Alameda County (Cooper). 



Subfamily JOUAFNETIN.E. 



Genus Pholadidea Goodall. 



Shell with a double anterior accessory plate (protoplax), the other plate present or absent, 

 the valves prolonged behind into leathery or testaceous cups or a tube (siphonoplax) for the protec- 

 tion of the siphons. 



Type, Pholadidea hscomhiana Goodall. 



Subgenus Pholadidea s. s. 



Shell with a double, rather small protoplax; the siphonoplax cup-like, the accessory plates 

 wanting; a single radial sulcus. 



Type, Pholadidea hscomhiana Goodall. 



m 



Section Peiiiiella Valenciennes. 

 Like Pholadidea^ but with a small mesoplax, the two parts of the protoplax confluent. 

 Type, Pholas penita Conrad. 



138. Pholadidea (Penitella) penita Conrad. 



Pholas pcnila Con., Jour. Phil. Acad. Nat. Sci., Vol. VII, 1837, p. 237, PI. XVIII, fig. 7, 



+ /'. concanierata Desh., 1840, -\-P. conradi Val., 1846 {fide Dall, Trans. Wagner 



Inst. Sci., Vol. Ill, Part 4, 1898, p. 819). 

 Parapholas penita CoN. , Cpr., Proc, Zool. Soc, 1856, p. 210. 

 Pholadidea penita CoN., Cpr., Brit. Assn. Rept., 1863, p. 637. Cooper, 7th Ann. Rept. Cal. St. 



Min., 1888, p. 259. Keep, West Coast Shells, p. 212, fig. 181, 1892. Williamson, 



Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 182. 

 Penitella petiita Co-^., Tryon, Proc. Phil. Acad. Nat. Sci., Monog. Pliolad., 1861, p. 87. 

 Penitella spelcea CoN. {fide Gabb, Pal. Cal., Vol. II, p. 88, 1869). 



