Raymond : Gastropoda of the Chazy Formation. 



181 



convex and the outer whorl concave, or the whole upper surface may 

 be convex and the spire somewhat elevated. The lower part of the 

 shell is usually rather long, the sides meeting the upper surface always 

 at less than a right angle ; in young shells, in rather an acute angle. 



The umbilicus is large in the cast, but in perfect specimens it is 

 filled by the shell. 



The surface is marked by lines which make a double curvature in 

 crossing the upper surface of the volution. They are interrupted at 

 the middle by a raised line. At the edge of the shell, which is acute, 

 there is a raised band on which the striae curve sharply back. 

 Beneath, the striae curve sharply forward, 

 then backward to the columella. 



In young shells the surface markings 

 consist of fine impressed lines which are 

 often more or less gathered into fascicles, 

 as is shown in figure 13, Plate XLVII, 

 and on Plate XLVII, figure 1. On 

 mature shells the surface of the body is 

 covered with coarse striae or undulations, 

 parallel to the successive positions of the 

 outer lip. This character of the surface 

 of the adult shell is shown in figures 5-8, 

 Plate LV. 



In fully adult shells the columella is 

 somewhat drawn out, twisted to the right, 



and slightly excavated. (See figure 8, Plate LV.) Some shells show 

 a hint of an umbilical perforation, as is seen in figure 7 on the same 

 plate, but in almost all cases this is covered by the columellar lip. 

 The outer lip seems always to be thin. Its form can be seen on Plate 

 LV, figures 5 and 6. 



For characters distinguishing this species from the last, see Rapliis- 

 toma striatum. 



Locality. — Shells of this species are common at Crown Point, Val- 

 cour Island, Valcour, and Chazy, New York, and Isle La Motte, Ver- 

 mont. The specimen represented on Plate XLVIII, figure 1 is in 

 the Carnegie Museum, figures n-13, Plate XLVII, and figures 2-6, 

 Plate XLVIII, are from shells in the Yale University Museum, and 

 those on Plate LV, figures 5-8 are from specimens in the United 

 States National Museum. 



Fig. 1. An enlargement of 

 the upper surface of a specimen 

 of Raphistoma stamineum Hall, 

 to show the band on the margin. 

 The striae turn back on the upper 

 surface, and then cross the angle 

 of the whorl before turning for- 

 ward again, and thus do not 

 make a true slit band, such as is 

 seen among the Pleurotomariidse. 



