168 PALAEONTOLOGY OF CALIFORNIA. 



LOXOTREMA, Gabb. 



L. TURRITA, n. S. 

 PL 28, Fig. 49. 



Shell elongated, turreted, spire elevated, nearly twice the 

 length of the aperture; whorls about six to six and a half, 

 slightly convex on the sides, abruptly truncated and flat on the 

 upper margin. Body whorl marked by eight or ten revolving 

 lines on the anterior half, crossed by sinuous lines of growth; 

 both sets of markings being very variable in distinctness in dif- 

 ferent specimens. Aperture obliquely subquadrate, bordered on 

 the inner side by a raised lip, the top retreatiug upwards, and 

 very obliquely backwards; outer lip thick above and below, very 

 thin in the middle, and with a strongly sinuous "margin, most 

 prominent near the anterior end ; inner lip thick, its margin 

 somewhat raised above the suface of the body whorl ; anterior 

 extremity of aperture not notched, but produced, and slightly 

 channelled. 



Length, 1.65 inch ; width of body whorl, .8 inch ; length of aperture (internal 

 measure), .6 inch ; width, .45 inch. 



Common in the Tejon Group, ten miles west of Griswold's, between San Juan 

 and New Idria. 



This very peculiar shell is evidently closely allied to Struthiolaria, but differs in 

 the shape of its volutions, the elevated spire, and the retreating backwards of the 

 posterior margin of the aperture. It has the characteristic lip-like anterior end 

 of that genus, and its sinuous outer lip. A marked character is the extreme thin- 

 ness of the middle of the whorl, and the equally unusual thickness of the walls 

 both above and below this point, rendering it almost impossible to obtain a speci- 

 men in which the middle of the outer lip is not broken away. 



ATRESIUS, N. Gen. 



Shell elongate, spire elevated; whorls rounded, aperture ovate, 

 slightly produced in front, outer lip entire, thin ; columella not 

 iucrusted, imperforate; surface marked by revolving ribs. 



