LOWER SILURIC SHALES OF THE MOHAWK VALLEY lOI 



can not distinguish it from specimens from Sacketts Harbor and 

 the writer has taken occasion to compare it with some of Hall's 

 types in the American Museum of Natural History. C . 1 e v a t a 

 is a middle Trenton species ; it has been cited from our Utica shale 

 and oth«er higher formations but probably erroneously. 



Ctenodonta declivis nov. 

 PL 6, fig. 2, 3 



Description. Shell small, acuminate, subovate, height by one-fifth 

 greater than the length, basal margin well rounded, nearly semi- 

 circular as in C . o b 1 i q u a , anterior dorsal margin slightly 

 concave, posterior dorsal margin convex. Beak prominent, situated 

 a little anterior of the center, curved backward; umbonal ridge 

 broad and little prominent, surface sloping gradually forward and 

 more abruptly backward, shell moderately convex, culminating 

 anteriorly of the center. Surface with faint growth lines. Interior 

 characters not observed. 



Position and locality. Olive gray, sandy shale of Snake Hill beds, 

 Snake hill. 



Remarks. C . declivis is in size and form closely allied to 

 C. obliqua (Hall), a species that is found in all groups of 

 the Cincinnati period. It differs from that species in being higher 

 and having the beak more anteriorly, but may in a revision of the 

 Ctenodontae be found to be but an earlier mutation of that long 

 ranged Western form. 



Ctenodonta prosseri nov. 

 PI. 6, fig. 4, 5 



Description. Shell small, moderately convex, broadly obliquely 

 subtriangular, well rounded in front and broadly rounded below, 

 narrow behind, with fairly large, prominent, incurved beaks, directed 

 i^posteriorly and situated a little anteriorly (about one-seventh of 

 length) of the middle; umbones carinate behind, the ridge slightly 

 ,:oncave in a side view. Hinge not seen. 



Position and locality. Snake Hill beds at Snake hill and other 

 olaces in Saratoga and Albany counties, N. Y. 

 [ Remarks. Doctor Ulrich has pointed out to us that this species 

 Is closely allied to his species C . s c o f i e 1 d i (title 39, page 593) 

 rem the Trenton and Galena shales of Minnesota. Our species 



