Casey — Notes on the Pleurotomidae. 159 



astonishing complex known as DriUia, do not belong even to 

 the present tribe and are true Pleurotomids. The genus 

 DriUia is in reality very limited, and, as far as known to me, 

 includes only its West African type species described by Gray 

 under the name umhilicata. The Clavini may be considered 

 to possess three principal types of structure or general facies 

 represented by Clavus, Crassispira and DriUia, but the 

 definition of genera in these sections will prove to be an 

 uncertain and rather unsatisfactorv matter. The genus 

 Ci/matosyrinx Dall, is a rather isolated fossil type, and is 

 truly represented only by lunata Lea, and a few other species 

 of our upper Tertiaries, having a peculiarly short, broad and 

 obtuse paucispiral embryo and an external oblique rostral 

 ridge. Many of the species placed with the type, even by 

 its author, do not belong there. Cossmann assumes the 

 name Cymatosyrinx for the old and very extensive genus 

 Clavus, on the ground of preoccupation, because of the older 

 name Clava Gm., but this is evidently inadmissible, Clavus 

 being abundantly distinct from Clava, and if such generic 

 words as these were not held to bf^ distinct, very great con- 

 fusion in zoological nomenclature would result. The species 

 figured by Tryon in his " Structural and Systematic Coucho- 

 logy " as a typical DriUia, the gibbosa of Kiener, does not 

 even belong to that section of the tribe, but should form the 

 type of a genus closely allied to the true Crassispira as rep- 

 resented by the West Indian bottaeVaX. and the West African 

 callosa Val. and carbonaria Rve. Although the shells in 

 this tribe are generally thick and heavy, it is remarkable that 

 some of the largest and heaviest of them, such as the three 

 species of Crassispira just mentioned, are seldom or neVer 

 found perfect when mature, but are invariably largely and 

 roughly decollated.' The following genus seems worthy of 

 definition at the present time, as it is quite isolated and one 

 of the oldest known types of the Clavini. 



Eodrillia n. gen. 



The typical forms of this genus are characterized by a 

 smooth, or at most finely and spirally striate surface, well 

 developed, more or less rounded ribs, which do not cross the 



