196 



Annals of the Carnegie Museum. 



lower part of the formation, where it is accompanied by Scalites angu- 

 latus, the other is just below the Camarotoechia plena beds, where it is 

 accompanied by a variety of fossils, the most prominent of which is 

 Pliomerops canadensis. It occurs most commonly as sections upon 

 the rock surface. 



Description. 



Shell large, coiled in one plane, umbilicated on both surfaces, all 

 the whorls visible. The whorls are broad, somewhat angular at the 

 sides, the last whorl moderately expanded at the mouth. Shell on 

 the whorls thin, but on the lip it becomes very thick and sometimes 

 corrugated. The surface is ornamented by coarse wavy revolving 

 striae which are crossed by transverse lines of growth. 



These lines turn backward in crossing the 

 middle of the shell and then forward again on 

 either side. Along the center of the shell runs 

 a narrow carina or slit band which is open for 

 a short distance on the last whorl. The lip 

 shows a broad, deep notch on the outer edge, 

 and at the base of this notch is a further pro- 

 longation in the shape of a narrow slit. On 

 most specimens this carina is a flat or depressed 

 band, but on a few, especially on young speci- 

 mens and on the outer whorl of adults, the 

 carina is elevated. 



One locality has furnished a number of very 



small specimens of this species, varying 1.5 to 



4 mm. in diameter. These young individuals 



always show more rotund whorls and a raised 



carina, but otherwise the same surface markings as the adult. (See 



figure 14, PI. LV. ) The adults are from 50 to 70 mm. in greatest 



diameter. 



Locality. — Common in the Chazy at Crown Point, Valcour Island, 

 Plattsburgh, and Chazy, New York ; and Isle La Motte, Vermont. 



Figures 3 and 4, Plate L, and figure 15, Plate XLIX, are from speci- 

 mens in the Carnegie Museum. Figures 16 and 17, Plate XLIX, and 

 figure 13, Plate LV, are from specimens in the United States National 

 Museum. Figure 14, Plate LV, is from a young specimen in the 

 Carnegie Museum. 



Fig. 5. An enlarge- 

 ment of a portion of the 

 surface of a specimen of 

 Bucania sulcatina (Em- 

 mons). 



