234 CALIFORNIA ACADEMY OF SCIENCES. 



A species varying principally in the number and prominence of transverse 

 ridges. Distinguishable from N. perpinguis by acuteness of spire. 



Found in all of the fossiliferous formations at all of the localities in the vicinity 

 of San Pedro. N. mendica is much rarer than the variety cooperi. Found in the 

 Pleistocene at the bath-house, Santa Barbara; at Barlow's ranch, and the old irri- 

 gating ditch, Ventura; and at Spanish Bight and Pacific Beach, San Diego. 



Living. — Sitka to San Diego (Cooper). 



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

 Barbara; Ventura; San Diego (Arnold). 



Pliocene. — Kirker's Pass; Twelve Mile House, San Mateo County; San 

 Diego well (Cooper): San Pedro (Arnold). 



223. Nassa mendica Gould, var. cooperi Forbes. 



Nassa cooperi Fbs. , Froc. Zool. Soc, 1850, p. 273, PI. XI, fig. 4. Cpr., Brit. Assn. Rept, 1863, 

 p. 662. Gabb, Pal. Cal., Vol. II, p. 74, 1869. Cooper, 7th Ann. Rept. Cal. St. Min., 

 18S8, p. 253. Keep, West Coast Shells, p. 37, fig. 18, 1892. 



JVassa metidica var. cooperi Fbs., Tryon, Man. Conch., Vol. IV, p. 56, PI. XVII, figs. 322,323, 

 1892. Williamson, Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 213. 



Shell like A/', mendica, except that the transverse ridges are more prominent and less 

 numerous. Mutations occur between the extreme N. mendica with latticed ornamentation consisting 

 of equally prominent spiral and transverse ridges, and the extreme N. cooperi with only six large, 

 transverse ribs. 



More common than the typical N. mendica. Found in the lower and upper 

 San Pedro series and Pliocene of the San Pedro region. Found in the Plei.stocene 

 at Pacific Beach, San Diego. 



Living. — Sitka to San Diego (Cooper): Catalina Island (Stearns). 



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

 (Stearns; Arnold). 



Pliocene. — Kirker's Pass; Twelve-mile House, San Mateo County; San 

 Diego well (Cooper): San Pedro (Arnold). 



224. Nassa perpinguis Hinds. 



Nassa perpinguis Hds., Voyage Sulphur, p. 36, PL IX, figs. 12, 13, 1844. Cpr., Brit. Assn. Rept., 

 1863, p. 662; Gabb, Pal. Cal., Vol. II, pp. 47, 75, 1869. Tryon, Man. Conch., Vol. IV, 

 p. 56, PI. XVII, fig. 319, 1882. Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 253. 

 Keep, West Coast Shells, p. 38, fig. 19, 1892. Williamson, Proc. U. S. Nat. Mus., 

 Vol. XV, 1892, p. 213. 



Nassa inierstriaia, Con., Pac. R. R. Rept, Vol. V, p. 327, PI. VI, fig. 49, 1856. 



Shell small, conical; spire elevated; apex subacute; whorls seven, convex, abruptly truncated 

 at posterior margin, forming a spiral table; ornamentation consists of sharp, spiral ridges with 

 slightly wider interspaces, and posteriorly sloping transverse ridges, the whole giving a decidedl)' 

 cancellate appearance to the surface; suture deeply impressed, distinct; aperture subovate; inner 



