INSTITUTE OF SCIENCE, PHILADELPHIA. 3 1 



geographical continuity. The recent representative or the latest fossil form 

 should preserve the stem-name because of the much greater opportunity of 

 determining its relations to the rest of the fauna and therefore, by implication 

 and analogy, that of the fossil representatives. 



The present species varies in stoutness or slenderness and in the strength 

 or weakness of the individual components of its sculpturing. The latter may 

 vary singly or in unison, and the number of combinations, even when color is 

 left unconsidered, is truly remarkable, as any one may verify by a very simple 

 mathematical calculation. It is a matter of taste how many of these combina- 

 tions should be named. 



Drillia abundans Conrad. 



Pleurotoma {Clavatida) abundans Conr., Journ. Acad. Nat. Sci. Phila. I., 2d ser., p. 115, pi. 



xi. fig. 25, 1848. 

 Drillia abundans Conr., Am. Journ. Conch. I., p. 19, 1S65. 



Later Eocene of Vicksburg, Mississippi; Pliocene of the Caloosahatchie 

 beds. 



When fully developed this species is about an inch long, with 12 to 14 

 sharp-edged ribs on the last whorl, a faintly internally lirate outer lip, and 

 about a dozen rather prominent spiral threads with much iiner spiral stria; in 

 the wide interspaces ; the most characteristic feature is the double oblique rip- 

 pling of a narrow band in front of the suture as it passes over the ribs of the 

 preceding whorl. It seems to be rare in the Caloosahatchie beds, and is not 

 known in a recent state. It is one of the most ancient representatives of the 

 ostrearuin type. 



Drillia abundans var. perrug-ata Dall. 



Caloosahatchie beds, not rare. 



This form differs from the type by attaining a greater size, by its more in- 

 flated whorls, by having nearly twice as many ribs, which are consequently 

 weaker, by its coarser and closer spiral threading, its less excavated and more 

 wrinkled anal fasciole, and the absence of lirae in the throat. I have received 

 some recent specimens from the Mexican coast which approach it very closely. 

 It reaches a length of 29.5, and a width of 8.0 mm. 



Drillia alesidota var. perspirata Dall. 

 Drillia alesidota Dall, Rep. Blake Gastr., pp. 84, 85, pi. x.xxvi. fig. i, 1889. 



Caloosahatchie beds. 



This form differs from the recent t3^pe and its var. inacilenta in its shorter 

 whorls, its proportionally greater stoutness, coarser and rounder spiral sculp- 

 ture, more constricted anal fasciole and stronger and more angular band be- 

 tween the fasciole and the suture. The number of whorls is about the same 

 in both. The maximum length of the fossil is about 29.0, and its width 

 lo.o mm. 



