312 CALIFORNIA ACADEMY OF SCIENCES. 



350. Hipponyx antiquatus Linnceus. 



Patella anfiquaius Linn., Syst. Nat., Ed. XII, p. 1259, 1768. Dillw., p. 1035, No. 44, 1760. 



Hipponyx antiquatus Yat^ia., Menke, Zeit. f. Mai., p. 79, 1853. Cpr., Proc. Zool. Soc, 1856, p. 3; 

 Brit. Assn. Rept., 1863, p. 654. Tryon, Man. Conch., Vol. VIII, p. 134, PI. XL, 

 figs. 93-99, 1886. Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 244. Keep, 

 West Coast Shells, p. 74, fig. 59, 1892. 



Concholepas antiquatus Linn., H. & A. Adams, Gen. Rec. Moll, Vol. I, p. 373, 1853. 



Shell obliquely conical; ape.x blunt, projecting beyond posterior margin of shell; surface 

 roughened by prominent lamellar, concentric lines of growth; base ovate; rim smooth, not crenated. 



This is a very variable species, the specimen described having an unusuall}' 

 elevated apex. The specimen was identified by Dr. Dall. 



Carj)enter believes the Hippony.v mitrula of the West Indian fauna to be 

 identical with the Bipponyx antiquatus of the Pacific Panama region. If these two 

 are identical it is another case of an old species which has lived on in both habitats, 

 having changed but little since the two regions were connected by water; or else it 

 is a case of parallel development, where two species, having come from a common 

 stock and living among like conditions, though separated geograjjhically, have 

 developed along parallel lines and are enough alike at the present time to warrant 

 their being called the same species. In such a genus as Hipponyx, where there are 

 so many mutations in a single species, either case would be possible. 



One specimen from the lower San Pedro series of Deadman Island; also found 

 in the Pliocene of Deadman Island. 



Living. — Bodega Bay and south; South America; Atlantic (Cooper). 



Pleistocene- — San Pedro (Cooper; Arnold). 



351. Hipponyx cranioides Carpenter. 



Hipponyx cranioides Cpr., Ann. & Mag. Nat. Hist., 3rd Sen, Vol. XIII, 1863, p. 428. Tryon, 

 Man. Conch., Vol. VIII, p. 135, PL XL, figs. 6, 7, 1886. Cooper, 7th Ann. Rept. 

 Cal. St. Min., 1888, p. 244. 



Shell obliquely conical, depressed; apex inconspicuous, blunt, posterior to center, but not 

 reaching margin; surface ornamented with several wide lamellae of growth which are grooved by 

 numerous radiating furrows; aperture ovate; rim thin, sometimes corrugated near outer edge; 

 interior smooth. 



Dimensions. — Long. 19 mm.; lat. 17 mm.; alt. 6 mm. 



Distinguishable from H. antiquatus by depressed shell, more central apex, 

 and more regular lamellae of growth, which are prominently radially furrowed. The 

 specimen described was identified by Dr. Dall. 



According to Tryon H. tumens equals H. cranioides. 



Rather common in the lower San Pedro series at Deadman Island and San 

 Pedro; rare in upper San Pedro series at Deadman Island and LosCerritos. Found 

 also in the Pleistocene at Spanish Bight, San Diego. 



Living.- — ^Straits of Fuca to Santa Barbara (Cooper). 



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



