ARNOLD — THE PALEONTOLOGY AND STRATIGRAPHY OF SAN PEDEO. 247 



outer lips, while others are strongly dentate. Of fifty specimens from the San Pedro 

 Pleistocene only three have the characteristic tooth developed, thus showing that in 

 these earlier forms this distinguishing characteristic was only occasional. The 

 scaly specimens are generally the strongest keeled. This latter form is the var. 

 spiratum of Blainville. 



Found in all of the lower and upper San Pedro series localities in the vicinity 

 of San Pedro. Found also in the Pleistocene at Barlow's ranch, Ventura; and at 

 Pacific Beach, San Diego. 



Living. — Baulinas Bay to San Diego (Cooper). 



Pleistocene. — San Pedro; San Diego (Cooper) : Lake Merced, San Mateo 

 County; San Pedro; San Diego; Ventura (Arnold). 



245. Monoceros lapilloides Conrad. 



Purpura {Monoceros) lapilloides Con., Jour. Phil. Acad. Nat. Sci., Vol. VII, 1837, p. 265, PL XX, 



fig. 18. 

 Mo7ioceros lapilloides Con., = M. punclaium Gray, -f- M. brevidens Con. {fide Cpr., Brit. Assn. 



Rept., 1863, p. 663). Keep, West Coast Shells, p. 28, fig. 9, 1892. Cooper, Bull. 



No. 4, Cal. St. Min. Bureau, 1894, Part 3, p. 28. 



Shell of medium size, purpuroid-shaped; spire elevated; apex subacute; whorls four, very 

 slightly conve.x; surface ornamented with nearly obsolete spiral cinguli and nearly obsolete, irregular, 

 wavy, transverse ridges; suture impressed, indistinct; aperture subovate; outer lip thickened, dentate; 

 inner lip flattened, smooth; canal short. 



Dime7isions. — Long. 20.5 mm.; lat. 13 mm.; body-whorl 18 mm.; aperture 14 mm.; defl. 

 67 degrees. 



The specimen described shows the reddish color of the live shells. Distin- 

 guishable from M. engonatum by much shorter spire, broader and shorter pillar, and 

 much less angular whorls; distinguishable from Purpura saxicola by relatively larger 

 spire, narrower aperture, dentate outer lip and spiral cinguli. 



Bare in uj^per San Pedro series of San Pedro; one specimen. 



Living. — Santa Barbara to San Diego (Carpenter): Monterey (Cooj^er). 



Pleistocene. — San Pedro (Arnold): Ventura County (Bowers). 



Genus Chorus Gray. 



Shell laminately varicose; spinose on the shoulder; canal rather long; outer lip with a spine 

 as in Monoceros. 



Tyjie, Chorus helcheri Hinds. 



246. Chorus belcheri Hinds. 



Murex belcheri Hds., Proc. Zool. Soc, 1843, p. 127; Voyage Sulphur, PI. II, figs. 1-3, 1S44. 



Pfeiffer, Nov. Conch., Ser. II, p. 35, PI. X, figs. 6, 7. 

 Chorus belcheri Hds., Cpr., Brit. Assn. Rept., 1863, p. 663. Tryon, Man. Conch., Vol. II, p. 198, 



PI. LXI, fig. 309, 1880; Syst. Conch., Vol. II, p. 114, PI. XLV, figs. 43, 44, 1883. 



Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 235. Keep, West Coast Shells, p. 25, 



fig. 7, 1892. Williamson, Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 216. 



