nt„„„^ . LAMELLTBBANCHIATA. 589 



Otenodonta carinata.] 



CtbnodontA oaeinata, n. sp. 



PLATE XLII, FIGS. 41-43. 



Shell rather small, gibbous in the anterior and rostral portions, the ends obtuse 

 m a dorsal view, the beaks large, prominent, strongly incurved, situated near the 

 midlength and turned decidedly toward the posterior end; the outline may be 

 described as subtriangular or obscurely quadrate; anterior margin most prominent 

 and strongly rounded in the lower half, the upper two-thirds more gently curved 

 and sloping backward to the beaks, being continuous with the antero-dorsal margin; 

 ventral margin straight or broadly sinuate, curving abruptly into the subtruncate 

 posterior margin and forming, with the latter, an angle of about 80° ; cardinal out- 

 line distinctly concave behind the beaks; post-cardinal region slightly produced, 

 though too blunt to be called alate; posterior umbonal ridge prominent, angular, 

 extending to the post- ventral angle; point of greatest convexity on. the rounded 

 anterior umbonal ridge; between the two ridges a wide, undefined sulcus, extending 

 from the umbones to the base. Surface marked with distinct and rather irregular 

 concentric lines of growth. Hinge plate arcuate, in other respects apparently as in 

 C. gihherula Salter. Shell thick, muscular scars not observed. 



C, gihherula is the only shell known to me with which C. carinata might be 

 compared. Although imperfectly known, I am quite confident that its affinities lie 

 chiefly with that species. Still, though the resemblances are sufiicient to prove that 

 the two forms belong to the same section of the genus, it is scarcely likely that any 

 one will fail to distinguish them specifically, the outline in the two species being 

 different in several respects. Thus," in C. carinata the posterior end is wider, the 

 post-cardinal region produced and subcuneate instead of flattened, the anterior 

 margin is more prominent below, and above curves more regularly into the dorsal 

 outline, while the basal margin is not so prominent anteriorly and on the whole 

 more nearly horizontal. The posterior umbonal ridge also is more prominent, the 

 mesial sulcus or flattening is a more pronounced feature and the anterior slope more 

 abrupt. Finally, the hinge plate is less bent and curved rather than geniculated. 



Formation and locality.— TAiAAle, Galena, about one mile east of Fountain, Minnesota.. 



Ctenodonta planodoesata TJlrich. 



PLATE XXXVII, FIGS. 25-28; PLATE XLII, FIGS. 38-40. 



Tellinomya planodomata Ulbich, 1892. Ninetpeth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 217. 



Shell small, moderately convex, subtriangular or trapezoidal, the hight, length 

 and thicknes, respectively, ten, fourteen and five mm.; beaks small, incurved, scarcely 

 projecting above the hinge, situated nearly one-third of the entire length from the 



