246 CALIFOKNIA ACADEMY OF SCIENCES. 



243. Murex (Pterorhytis) monoceros Soirerby. 



Murex monoceros Sby., Proc. Zool. Soc, 1840, p. 143. Tryon, Man. Conch., Vol. II, p. 115, 



PI. XXXV, figs. 3S8, 389, 1880. 

 Muriddea {Phyllouotus) paucivaricata Gabb, Pal. Cal., Vol. II, p. 43, PI. XIV, fig. i, 1869 {Jide 



Tryon). 

 Muriddea paudvaricata Gabb, Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 252 {fide Tryon). 



Shell moderate in size, fusiform; spire nearly as long as aperture; whorls seven, subangulated, 

 bearing eight or nine large, longitudinal 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 squamose plates; body-whorl sometimes 

 ornamented with five or six, quite prominent, rounded, spiral ridges. 



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

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



Distinguishable from M. californica by denticulated outer lip, lack of varices, 

 thicker shell, and generally larger size. Originally described from Pleistocene 

 specimen. 



Rare in upper San Pedro series of San Pedro. 



Living. — Lower California? 



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



Genus Monoceros Lamarck. 



Shell ovate; last whorl large; spire rather elevated; aperture semilunar; inner li]) wide and 

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



Monoceros lugiihre Sowb. is a characteristic species. 



244. Monoceros engonatum Conrad. 



Monoceros engonatum 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 vShells, p. 29, fig. 10, 1892. Willi- 

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



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



Shell of medium size, fusiform; whorls six, angular, flattened to concave above and below; 

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

 elliptical; outer lip eflTuse, 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. 

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

 which approach very near to M. lapilloides. Some specimens have thin and smooth 



