GASTEROPODA OF THE LOWER GEBEN MAELS. 137 



perforation, representing the comparatively slender solid columella; the 

 base of the cast is marked by a rather deep, narrow, spiral groove, about 

 one-third to one-fourth of the width of the volution from the umbilical 

 cavity, marking the position of an internal spiral ridge at this point on the 

 inside of the basal portion of the shell; volutions flattened in the direction 

 of the spire, with moderately distinct suture lines separating them in the 

 casts, their surfaces closely and deeply scarred by the attachment of foreign 

 substances to the outside of the shell during life. 



This species has generally been considered the same as the Trochus 

 leprosus of Morton, Xenophera leprosus of this work, but was described as a 

 distinct species, first by Dr. Tuomey, and subsequently made the type of 

 the genus Endoptygma by Mr. Gabb. I do not think it is always an easy 

 matter to distinguish them, as the groove may not always be present, and 

 in other respects there are no constant differences that I can discover. On 

 one large cast, which I have referred to Morton's species, there is an indica- 

 tion that the apertural ridge was just appearing, while in the younger 

 stages of the shell no evidence of its existence appears. In much younger 

 individuals of this form it is strongly marked. It may be that both forms 

 should be referred to the same species, in which case the present genus 

 would have to be abandoned. 



Formation and locality: In marls of the Lower Beds near Burlington, 

 New Jersey. 



SCALAEIIDtE. 

 Genus SOALAKIA Lamarck. 



SCA.LAEIA (OpALIA) ThOMASI ? 



Plate xviii, Fig. 1. 

 Scala (Opalia) Thomasi Gabb : Proc. Acad. Nat. Sci., Phila., 1876, p. 396. 



Shell slender, turreted, whorls numerous, closely coiled and very ven- 

 tricose, with rather close sutures, numbering seven or more in a specimen 

 of less than seven-eighths of an inch in length; apical angle less than 30°, 

 probably not more than 25°, the specimen being too imperfect to allow of 

 positive measurement; aperture apparently round and the base of the volu- 



