184 CALIFOUNIA ACADEMY OF SCIENCES. 



137. Zirphaea gabbii Try on. 



Zirpheea gabbii'YVi\o^,Vroc. 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. 



Zirphcea crispata (non Lixn., 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. 



Dimejisions. — Long. 72 mm.; alt. 35 mm.; diam. 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 San Pedro, Los Cerritos, Craw- 

 fish George's, and Deadman Island. 



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



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



Subfamily JOUANNETIN^. 



Genus Pholadidea Goodull. 



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 loscomhiana 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 loscombiana Goodall. 



Section Pen'ddln 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 penita Con., Jour. Phil. Acad. Nat. Scl, Vol. VII, 1837, p. 237, Pi. XVIII, fig. 7, 



■\-P. concamerala Desk., 1840, -\-P. cojiradi Val., 1S46 {fide Dall, Trans. Wagner 



Inst. Sci., Vol. Ill, Part 4, 1898, p. S19). 

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

 Pholadidea penita Qos-i., 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. 1S2. 

 Penitella penita Con., Tryon, Proc. Phil. Acad. Nat. Sci., Monog. Pholad., 1861, p. 87. 

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



