Raymond : Gastropoda of the Chazy Formation. 



185 



This specimen was very kindly loaned for study by Dr. E. O. Hovey 

 and Professor R. P. Whitfield of that Museum, and the accompanying 

 text figures illustrate its characters. The spire has been almost entirely 

 weathered off, but the body whorl retains a part of the shell. The 

 specimen has been mutilated along the inner lip and columella, but 

 enough of the shell is retained to show that the form of the aperture 

 was essentially similar to that in Raphistoma stamineum. The striae 

 on the top of the whorls cross the surface in an uninterrupted sweep, 

 thus differing from Raphistoma. The only other genus with which 

 this shell could be compared is Trochonema, but the absence of a 

 revolving flattened band and of the umbilicus, will readily distinguish 

 it from that group of shells. 



Description. 



Shell large, robust, making about 

 five volutions. Whorls strongly 

 angulated, flattened on top. Spire 

 rather high, frequently making up 

 nearly half the height of the shell. 

 The initial whorls are rounded in 

 cross section, the succeeding whorls 

 increasing rapidly in size to the 

 body whorl, which always consti- 

 tutes at least half the shell. In 

 some individuals the slope from the 

 suture to the periphery is rather 

 steep, in others it is flat or slightly 

 concave. Below the peripheral 

 angle is a narrow concave band, 

 best shown in the cast. The body 

 whorl is drawn out below, some- 

 what cylindrical. Complete aper- 

 ture not observed, but apparently 

 the same as in Raphistoma stam- 

 ineum. The inner lip is thickened, 



wide, turned back over the columella. In front the lip is thickened, 

 rounded and entire, not canaliculate. The outer lip seems to be thin 

 and the most perfect margin seen — that on the specimen in the 

 American Museum — is approximately parallel to the lines of growth 

 as in Raphistoma. 



Fig. 4. Outline drawing of the 

 same specimen illustrated by figure 3. 

 The shell has been largely removed 

 from this side of the specimen, but the 

 former shape of the outer lip is indi- 

 cated on the cast, as shown here. The 

 irregular double line represents the 

 broken edge of the shell, and the 

 smooth line the margin of the lip. 

 Natural size. 



