292 CALIFORNIA ACADEMY OF SCIENCES. 



rounded, equal, equidistant ridj^es; spiral sculpture hardly visible; suture deeply impressed, distinct; 

 aperture subrotund; outer lip thin, smooth; columella smooth; body-whorl anjjulated at the base; 

 base shows spiral lines. 



Dimensions. — Long. 6 mm.; lat. 2.2 mm.; body-whorl 2.5 mm.; aperture 1 mm.; defl. 

 24 degrees. 



This species, with the pos.sible exception of B. williamsoni, is the smallest of 

 the Pleistocene Bittiums of this looality, ami is easily di.stinguishahle by its size and 

 the faintness of its spiral sciili)tiire. 8evei-al specimens show a slightly less deflection 

 than the one figured. Specimen identified by Dr. Dall. 



Kare in the lower San Pedro series at San Pedro. The specimen figured, 

 which was found in tlie lower San Pedro series at San Pedro, is now in the collec- 

 tion of Delos Arnold. 



Pleistocene. — San Pedro (Arnold). 



317. Bittium filosum Gould. 



Cerithiutn /ilosum Old., Proc. Bost. Soc. Nat. Hist., Vol. Ill, 1849, p. 120; Wilkes' Expl. Exped., 



Vol. XII, p. 149, fig. 175, 1852. 

 BUtititn Jilosum Gld.. Cpr., Brit. Assn. Rept., 1863, p. 655. Tryon, Man. Conch., Vol. IX, 



p. 152, PI. XXIX, fig. 90, 1887. Cooper, -th Ann. Rept. Cal. St. Min., 1888, p. 230. 



Keep, West Coast Shells, p. 72, fig. 57, 1S92. 



Shell small, slender, turreted; apex elevated, acute; whorls eight, flat, slightly angulated 

 near anterior margin, and ornamented with four alternating ridges and grooves of about equal width; 

 apical whorls transversely sculptured; base of body- whorl sculptured in same way; suture deep, 

 distinct; aperture small, semielliptical, with basal emargination instead of a canal; lip thin, with 

 interior ridges corresponding to exterior grooves. 



Dimensions. — Long. 8.5 mm.; lat. 2.9 mm.; aperture 2 mm. x 1.2 mm.; defl. 20 degrees. 



This species is distinguishable by its lack of transverse ornamentation. The 

 specimen described was identified by Dr. Dall. 



Specimens of this species are rather rare in both the lower and upper San 

 Pedro series at San Pedro and Deadman Island; a few found at Crawfish George's. 



Living. — Sitka to Monterey (Cooper). 



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



318. Bittium quadnfilatum Carpenter. 



Plate IX, Fic. 2. 



Bittium quadrifilatuni CPR., Brit. Assn. Rept., 1863, p. 655; Jour, de Conch., Vol. XII, 1865, p. 143. 

 Tryon, Man. Conch., Vol. IX, p. 153, PI. XXIX, fig. 91, 1887. Cooper, 7th Ann. 

 Rept. Cal. St. Min., 1888, p. 230. Keep, West Coast Shells, p. 72, 1892. William- 

 son, Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 205, PI. XXI, fig. 4. 



Shell small, turreted, elongate; apex acute; whorls ten or eleven, nearly flat; body-whorl 

 slightly ventricose; surface sculptured by four more or less prominent spiral ridges, and on upper 

 whorls by transverse ridges; these ridges become obsolete on the penultimate and body-whorls in 

 adult specimens, leaving only the spiral lines on these whorls; suture distinct, impressed, giving a 



