152 PALAEONTOLOGY OF CALIFORNIA. 



The general form, and the notch at the upper part of the outer lip, place this 

 genus, without question, in the Plewotomidce, but its thick shell, low spire, and 

 very broad body volution, separate it unmistakably from all the known genera of 

 the family. 



H. TROCHOIDEA, 11. 8. 

 PI. 26, Fig. 30, 30 a. 



Shell depressed fusiform, spire low, whorls five and a half, 

 concave above, body whorl bicarinate, each carina bearing a row 

 of large rounded tubercles ; suture linear, undulated, the upper 

 margin of each whorl being attached to the upper row of tuber- 

 cles on the preceding volution ; between the two carinas on the 

 body whorl, the surface is obliquely concave ; anteriorly it is deeply 

 excavated and produced in a long straight canal. Aperture broad 

 above, narrow and straight below; outer lip simple, broadly emar- 

 ginate on the upper surface, inner lip incrusted. Surface orna- 

 mented, besides the tubercles, by minute revolving lines, smaller 

 above than below, and showing a tendency in advance, to alter- 

 nation in size. 



Length, restored from lines of growth, .9 inch; width of body volution, .6 

 inch ; length of aperture, .65 inch. 



Rare in the Martinez Group, Martinez; Mathewson. 



BEL A, Leach. 



B. CLATHRATA, 11. S. 

 PI. 26, Fig. 31. 



Shell small, subfusiform; spire elevated, whorls six, the first 

 1| — 2 nuclear, rounded, smooth ; the others angular, flat, or 

 slightly concave on the sides, and sloping above a little concave 

 to plane ; body whorl excavated below, bicarinate in the middle. 

 Aperture moderately broad, tapering slightly in advance ; outer 

 lip simple, broadly excavated above, and slightly prominent in 

 the middle ; inner lip slightly incrusted. Surface marked by two 



