Raymond: Pelecypoda of Chazy Formation. 331 



Island. All the other specimens, which are fairly numerous, are casts 

 of the exterior of single valves. In the present paper, the shorter and 

 higher end of the shell is called the front of Cteiwdonta, while in the 

 original description, the longer end, toward which the beaks point, 

 was considered the front. 



Dcscriptiou. 



Shell small, depressed convex, thickest at the umbos, longer than 

 high, the beak situated at about one-third the length. The posterior 

 end is somewhat drawn out, as in Ctenodonta nasuta Hall. Greatest 

 convexity at the umbo, the anterior slope steep, posterior slope very 

 gradual. Both slopes to the hinge abrupt, but that to the basal 

 margin gentle. The interior of a right valve shows the teeth in a 

 gently curved, uninterrupted series, nine teeth in front, and seven 

 behind the beak. A large specimen is 12 mm. long and 9 mm. high. 



This species resembles those specimens of Ctenodonta levata (Hall) 

 which are represented by figures 1/ to i of the plate cited in the 

 synonymy we have given, but are unlike figures la to ic. There seem 

 to be fewer teeth on the hinge than in C. levata. 



Locality. — Rather common in the trilobite layers of the Middle 

 Chazy on Valcour Island, and at the same horizon at Crown Point. 

 Also in the Upper Chazy on Valcour Island. 



2. Ctenodonta dubiaformis Raymond. (Plate XXIX, figure 6.) 



Ctenodonta dubiaformis Raymond, American Journal of Science, (Ser. 4), Vol. XX, 

 1905. P- 371- 

 The outline of this species resembles the smaller specimens of 

 Ctenodonta dubia figured by Hall, and it plainly belongs to the same 

 group. It is, however, higher in proportion to the length. 



Description. 



Shell small, moderately convex, beak sub-central. Greatest con- 

 vexity at the umbo, the slope from it to the base being nearly fiat. 

 Basal margin nearly straight. Posterior end nasute, and a little longer 

 than the anterior end, which is regularly rounded. 



All the specimens are casts, without trace of hinge teeth, muscle 

 scars, or surface markings. The largest specimen is 19 mm. long and 

 10.5 mm. high. Another is 17 mm. long and 9 mm. high. 



Locality. — Sloop Bay, Valcour Island, in the middle of the Chazy. 



