278 PALEONTOLOGY OF NEW YORK. 



elongate form, more regularly convex umbonal slope, more regularly rounded 

 posterior extremity, and narrower anterior end. 



This is probably the species described by Mr. Conrad as Cypricardites myti- 

 loides, of which he gives the following description : 



" C. mytiloides. Ovate, slightly ventricose ; lines of growth prominent; umbo 

 prominent ; dorsal margin elevated ; anterior basal margin very oblique and 

 slightly contnicted ; posterior side profoundly dilated and the margins regularly 

 rounded. Locality. Near Ogden's Ferry, tab. of forui. No. 2o." 



Formation and localities. In the shales of the Hamilton group ; jjrincipally in 



the eastern and central portion of the State, on the shores of Seneca and 



Cayuga lakes. 



MODIOMORPHA ALTA. 

 PLATK XXXVII, FIGS 1, 2 (4, 5, 6?), 7-li, l."!, 16; ANI> PLATE LXXX, FIG. 7. 



Cypricarditts alta, Conrau. Geol. Surv. N. Y., Ann. Rep., p. 52. 1841. 

 JUtidiomorpha alta, (Conbad) Hall. Prelim. Notice Lamellibranchiata, 2, p. 75. 1870. 



" " " " Pal. N. Y., vol. V, pt. 1. Plates and Explanations : PI. 37, figs. 1-16 ; 



pi. 80, fig. 7. 1883. 



Shell larger than the medium size, broad, rhomboid-ovate ; length one-third 

 greater than the height ; the basal margin for two-thirds of its length from 

 the anterior curve is nearly straight, varying from slightly concave to nearly 

 straight, abruptly curving at the post-basal extremity, and continuing to the 

 post-cardinal margin in an oblique, gently curved outline. In some examples 

 the posterior margin is regularly curved, cardinal margin sometimes form- 

 ing a nearly straight line, usually gently arcuate. Anterior end produced 

 beyond the beak from one-sixth to one-fourth the length of the shell, 

 obliquely truncated, obtuse, rounded below ; its greatest extension is below 

 the middle of the shell. 



Valves convex, gibbous on the umbonal and medial portions of the 

 shell ; the umbonal ridge is gibbous and arched upward ; the point of 

 greatest convexity is about the middle of the shell or a little posterior. 

 The depth of both valves is equal to two-thirds of the height of the shell. 



Hinge-line straight, oblique, extending for less than half the length of 

 the shell. 



