96 BULLETIN 111, UNITED STATES NATIONAL MUSEUM. 



specific characters, but appear to be wholly individual and possibly 

 pathologic. Sculpture is sometimes mentioned by authors, but al- 

 most apologetically. In a few cases, notably in Cadulus acus, the 

 alternate rings of more and less dense shelly deposit present a sur- 

 face that might possibly be referred to as sculptured, but it is not a 

 true sculpture in the sense employed in descriptions of Dentalium. 



The words ''dorsal" and "ventral" are employed in descriptions of 

 Cadulus to mean the convex and the concave sides or arc of the shell, 

 dorsal being the convex side. There is, however, a difference of opin- 

 ion as to which side is actually dorsal or truly ventral as in conformity 

 with the "back" or "front" of the animal. 



Measurements of the "arc," as the term is used in the descriptions 

 of Dentalium, will be omitted, as the small size of the shell and 

 irregular lines of curvature do not lend themselves well to this 

 feature of diagnosis. The important specific characters of the Caduli 

 are the slits and lobes about the edge of the apical orifice, referred 

 to as "apical characters," the general shape of the shell as deter- 

 mined by the position of the equator (section of maximum diameter) ; 

 the ratio of length to breadth; the localized or general type of swell- 

 ing; the compression (either lateral or dorso-ventral) of the shell; 

 the obliquity of the aperture; and, lastly, the size. Thus these little 

 colorless shells possess more characters than at first seem possible. 

 A good way to proceed in identifying material is to examine first the 

 apical characters in order to place the shells in their proper subgeneric 

 groups. Then seek among the figured species of about a similar size 

 for those that have median or submedian equators or with equators 

 more anteriorly placed. These are the important points of resem- 

 blance to be first established, after which the oval or round section, 

 the small or large apical orifice, and the obliquity of the aperture, 

 follow. Geographic and temperature ranges are especially important 

 and should be kept always in mind when seeking to determine 

 material. In a general way it may be' said that the large and medium 

 sized species fall under Flatyschides, the small and slender forms 

 under Gadila, the small bulbous species under Cadulus, while those 

 of very prominent deep apical slits are Polyschides. 



Subgenus POLYSCHIDES Pilsbry and Sharp, 1898. 

 1898. Polyschides Pilsbry and Sharp, Tryon's Man. Conch., vol. 17, p. 148. 



The shell is inflated above [anterior to], the middle or not much 

 bulging; the apex is cut into a number of lobes, generally four, by as 

 many slits. 



Genotype. — Cadulus tetraschistus Watson. For enlarged drawing of 

 apical characters of Polyschides see plate 17, figure 7. 



The chief characters of the subgenus are the deep slits and promi- 

 nent apical lobes. In all the species coming within our notice these 

 apical lobes are four in number. 



