Raymond: Gastropoda of the Chazy Formation. 179 



Raphistoma striata Hall, 1847, Paleontology of New York, Vol. I, 



p. 28, PI. 6, figs. 2a, 2b. 

 Scalites striata Emmons, 1855, American Geology, Vol. I, PI. 4, fig. 30. 



Description. 



Shell large, high, spire nearly flat, although the inner volutions are 

 sometimes a little elevated. There are usually four or five volutions 

 which expand gradually, but more rapidly than in Raphistoma stamin- 

 eum. The angle between the upper side and the outer surface of the last 

 volution is always large, varying from 75 to 90 , and the shoulder be- 

 tween the two is always quite sharp, while in Raphistoma stamineum 

 it is apt to be considerably rounded. The umbilicus is small in the 

 cast and completely closed in specimens retaining the shell. As in 

 Maclurites, the angle in the cast, between the basal portion of the 

 shell and the inner surface of the umbilicus, is sharp. 



The surface, when perfect, is marked by numerous, rather coarse, 

 rounded striae, or rather undulations. Starting from the suture they 

 run sharply backward until stopped by the low revolving line charac- 

 teristic of the genus. Starting again on the other side of this line, 

 they run back to the margin, which they meet at an acute angle. Be- 

 low the margin they swing sharply forward, and a little below the 

 middle of the slope they turn back again under the thickened inner 

 lip which covers the columella. Around the margin of the upper sur- 

 face of the whorl is the slit band similar to that described by Billings 

 in Pleurotomaria docens. However, the striae do not cross it in loops 

 as indicated in his figures, but, on reaching it, turn more sharply back- 

 ward, and turn forward again only after crossing the angle of the shell. 



The specimens most commonly found are casts retaining little or 

 none of the shell. In this condition they resemble specimens of Ma- 

 clurites magnus but may readily be distinguished from that shell by 

 the dextral instead of the sinistral coil. They differ from exfoliated 

 specimens of Raphistoma stamineum in having the sides more nearly 

 at right angles to the top, in the more rapid expansion of the whorls, 

 the smaller umbilicus, and in the sharp angle of the lower surface of 

 the whorls bordering the umbilicus. The cast of Raphistoma stamin- 

 eum is rounded, while that of Raphistoma striatum is angular. 



Locality. — Fairly common at Valcour Island. Rare at Chazy, 

 New York, and at Aylmer, Province of Quebec, in the Aylmer 

 Sandstone. 



