2-l<5 I'ALIl'OKNIA ACADEMY OF SflRNCKS. 



243. Murex (Pterorhytis) monoceros Suircvby. 



Afurex monoceros Shy., Proc. Zool. Soc, 1S40, p. 143. Tryon, Man. Conch , Vol. II, p. 115, 



PI. XXXV, fitjs. 3SS, 389, iSSo. 

 Miiricidea (^Phylloyiotus) paucivarkata Gabb, Pal. Cal., Vol. II, ]). 43, PI. Xl\', tig. i, 1S69 (^fide 



Tryon). 

 Afuricidea paucivaricata Gabb, Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 252 (^fide Tryon). 



Shell moderate in size, fusiform; spire nearly as long as ai)ertiiri-; whorls seven, subangulated, 

 bearing eight or nine large, longitiulinal ribs which develop into prominent nodes on the angle; 

 suture irregular, appressed, distinct; aperture ovate; canal rather short, narrow, recurved, and often 

 overgrown by two lips; outer lip thickened, denticulated with four sharp teeth; inner lip slightly 

 projecting, smooth, incrusted; columella widened; varices two or three, never prominent, sometimes 

 obsolete; numerous small revolving ribs crossed by small squamosa plates; body-whorl sometimes 

 ornamented with five or si.\, quite prominent, rounded, spiral ridges. 



Dimensions. — Long. 46 mm.; lat. 23 mm.; body-whorl 32 mm,; aiK-rliirc, including canal, 

 26 mm.; canal 9 mm.; defl. 50 degrees. 



Distingiiislia})le from M. californica by dcnticnliitcd outer lip, lack of varices, 

 thicker .'^liell, and generally larger size. Originally de-scribod from Pleistocene 

 specimen. 



Rare in upper San Pedro series of San Pedro. 



Living. — Lower California? 



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



Genus Monoceros Lamarck. 



Shell ovate; last whorl large; spire rather elevated; aperture semilunar; inner \\p wide and 

 flattened; outer lip crenated, with a prominent tooth usually at the forepart. 



Monoceros lugiihre Sowb. is a characteristic sj)ecies. 



244. Monoceros engonatum Conrad. 



Monoceros engonahnn Con., Jour. Phil. Acad. Nat. Sci., Vol. VII, 1837, p. 264, PI. XX, fig. 17. 

 Cpr., Brit. Assn. Rept., 1863, p. 663. Gabb, Pal. Cal, Vol. II, p. 75, 1869. Tryon, 

 Man. Conch., Vol. II, p. 195, PI. LXI, figs. 304, 1880. Cooper, 7th Ann. Rept. 

 Cal. St. Min., 1888, p. 251. Keep, West Coast Shells, p. 29, fig. 10, 1892. Willi- 

 amson, Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 214. 



Monoceros unicarinatum RvE., Icon. Conch., Sp. i. 



Shell of medium size, fusiform; whorls si.\, angular, flattened to concave above and below; 

 spirally sulcata, sulci with tranverse lamellar striae; suture deeply appressed, distinct; aperture sub- 

 elliptical; outer lip effuse, dentate within; inner lip slightly flattened, smooth; canal deep, narrow, 

 recurved; pillar twisted, squamose. 



Dimensions. — Long. 40 mm. ; lat. 20 mm.; body-whorl, 30.5 mm.; aperture 24 mm.; defl. 

 55 degrees. 



This is a variable species. Specimens showing the scaly surface of var. 

 spirntum grade over into tiie smooth form; the sharp-keeled forms merge into those 

 which approach very near to J/, lapilloides. Some specimens have thin and smooth 



