Casey — Notes on the Pleurotomidae. 153 
Tropisurcula n. gen. 
The shell in this genus is small in size, of slender form, 
with moderately elongate and slender beak and narrow, 
closely coiled, multispiral embryo, which is higher than wide, 
and perfectly smooth and polished throughout. The ribs 
are about equal in number to those of Pleurofusia but cul- 
minate in transverse prominences at the summit of an angu- 
late median periphery, and sometimes become gradually 
feebler on the larger whorls. The spiral lines are subequal 
among themselves, relatively rather coarse but low, and very 
close-set throughout. The species known to me are two in 
number as distinguished by the following characters : — 
Ribs nine to ten in number, rounded and distinct throughout the length of 
the whorls, though much more prominent on the peripheral ridge and 
tending to become extinct on the broad fasciolar surface of the larger 
whorls; spiral lines coarse but not much elevated, even above, coarser 
and usually separated by a fine line below, the periphery; apex of 
the embryo obtuse. Length of a specimen of 5 body whorls, 10 
mm.; width, 2.9 mm. Red Bluff Eocene to the Vicksburg 
Oligocene......... w sinieia) tices weisiaee esieey a cia caseyi Ald. 
Ribs seven or eleut in ihe more a broadly rounded, very prominent on 
the angulate periphery, becoming rapidly obsolete below, and usually 
wholly effaced on the fasciolar surface above, the periphery, especially 
on the larger whorls; spirals rather wide but feebly elevated, close-set 
and subequal throughout, but still feebler on the fasciolar surface; 
embryo acute at tip, of five smooth and highly polished whorls, narrow- 
ing more rapidly above the two basal whorls, the apical very small. 
Length of a specimen of 4 body whorls, 7.6 mm.; width, 2.6 mm. 
Lower Claiborne Eocene of St. Maurice, La............crenula n. sp. 
The embryo in caseyi is much more evenly and feebly 
tapering from base to apex than in crenula. The former 
species was described by Mr. Aldrich under the generic name 
Drillia. 
Surculoma nh. gen. 
The type of this genus was regarded by Cossmann as a 
member of his genus Amblyacrum, and, while the small pauci- 
spiral embryo is very nearly the same in general form, all the 
other characters differ to so great a degree that it is not easy 
