Raymond : Gastropoda of the Chazy Formation. 205 



in being higher in proportion to the width and in having the upper 

 surface of the whorls slightly convex instead of concave. 



Locality. — Common in the Aylmer Limestone at Aylmer and at 

 the Hog's Back, near Ottawa, Canada. The type is in the Yale Uni- 

 versity Museum. 



Family Trochonematid^e Zittel. 



Genus Trochonema Salter. 



Trochonema biangulatum (Hall). 



(Plate LIII, figures 9, 10.) 



Pleurotomaria biangulata Hall, 1847, Paleontology New York, Vol. 



I, p. 31, PL 6, figs. 6a, 6b. 



The type of this species cannot now be located, but there are speci- 

 mens in the Hall collection in the American Museum of Natural His- 

 tory labeled Pleurotomaria biangulata which agree fairly well with 

 the original description and figure and may, perhaps, be accepted as 

 authentic examples of Hall's species. The shells so labeled are small, 

 flattened, with few volutions, and, although they show no surface 

 markings, they apparently belong to the genus Trochonema. At 

 Valcour Island this small gastropod occurs sparingly in two or three 

 localities and may be readily separated from all other species of 

 Trochonema in the Chazy by its small size, few whorls and small 

 umbilicus. Its nearest ally in the Chazy is Trochonema dispar, but it 

 is readily distinguished from that shell by its small umbilicus and its 

 square-shouldered whorls. 



Description. 



Shell small, with about three whorls which expand gradually. 

 Spire low, raised very little above the body whorl. Body whorl with 

 two carinae, which are about equally distant from the axis of the shell, 

 thus forming the flattened side of the whorl usually seen in this genus. 

 Upper surface of the whorl slightly convex, often almost flat. Lower 

 surface gently convex. Umbilicus small. All specimens are casts, 

 and show no traces of surface markings. One specimen is 10 mm. in 

 greater diameter and 7 mm. high. The body whorl is 3.5 mm. wide 

 at the aperture. Other specimens are of about the same size, one or 

 two being sliglitly larger. 



Locality. — This species occurs in the Chazy at Valcour Island, 

 New York. The figured specimen is in the Yale University Museum. 

 It is from the south end of Valcour Island. 



