Casey — Notes on the Pleurotomidae. 147 



and covered with rather close-set, fine but sharply elevated threads, the 

 one nearest the peripheral carina much the largest; surface below the 

 peripheral carina cylindric, with a similar carina a little below its mid- 

 dle and another near the lower edge; space between the peripheral 

 carina and the one next below with a finer carina a little below its mid- 

 dle. Length of a fragment consisting of the embryo and 4 spire whorls, 

 5.6 mm.; width, 3 mm. Lower Claiborne Eocene of St. Maurice, 

 La helicoidea n. sp. 



Mr. Aldrich mentions no creuulation on the periphery of 

 the nepionic whorls of tuomeyi^ but these are said to exist 

 by Prof. Harris. 



Batbytoma Harr. et Burr. 



Dolichotoma Bell. (nom. praeocc). 



According to Cossmann, this genus exists fossilized in all 

 the Tertiary strata and is also found living, but I am inclined 

 to believe that that author has confused a number of generic 

 or subgeneric types and that the really typical BatJtytoma 

 occurs only in the upper European Tertiaries, where it is 

 represented by Murex cataphracius Broc. The geologically 

 much older American species, from the upper Eocene of Red 

 Bluff and the Vicksburg Oligocene, described by Conrad under 

 the name Pleurotoma congesta, is a much smaller species and 

 differs in some respects, perhaps subgenericall}-, but may be 

 considered a Bathytoma for the present. The peripheral ridge 

 is much better marked than in Megasurcula and is frejqueutly 

 costulose and the obtuse oblique columellar ridge, very feeble 

 in Megasurcula is conspicuous in at least the American Bathy- 

 toma congesta. This ridge is not homologous with the colu- 

 mellar plicae of some other genera, which are doubtless to be 

 closely associated in any natural arrangement, such as Sco- 

 bineUa, and, occurring much lower down on the columella, is 

 probably different in origin and significance. 



Megasurcula n. gen. 



The embryo in this genus is apparently paucispiral, but con- 

 oidal, the canal obsolete, the base of the shell broadly obtuse, 

 the pillar with an oblique ridge externally ; sinus large and 



