284 PALEONTOLOGY OF NEW YORK. 



A medium-sized specimen has a length of 38 mm., and a height of 23 

 mm. A hirge individual mejisures 53 mm. in length and 29 mm. in height. 



This species differs from any of the preceding forms in the more nearly 

 parallel cardinal and basal margins, in the angidar umbonal ridge, more direct 

 truncation of the posterior end, and the obsolescence of the strias on the um- 

 bonal region. As compared with M. rigida the basal margin is straighter, the 

 anterior end is wider, and the cardinal line less oblique. 



Formation and localities. In the middle and upper portions of the Hamilton 

 group, at numerous localities in the central and western part of the State. 



MoDiOMORPHA SUBALATA, var. Chemungensis, n. var. 



PLATE XLI, FIGS. 5, 6, 8, 9, 11 (7, 10?) ; AND PLATE XXXIX, FIG. 15. 



Modioinorpha rigida, in part. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 41, Bjfs. 10, 



11. 18S3. 



This variety includes the specimens from the Chemung group, and presents 

 the principal characteristics of the species. The forms are longer in proportion 

 to their height, the cardinal line less oblique, the posterior extremity usually 

 more rounded, the umbonal slope more arcuate, and the striae are filiform, 

 sharper and more regular. Although presenting these differences, it does not 

 appear advisable to propose a distinct specific name. 



The specimens present considerable variety among themselves, as is seen by 

 reference to figs. 6, 7 and 10 of plate xli as compared with figs. 5 and 11 of 

 the same plate. A larger collection of specimens may afford the means of 

 a more positive separation of these forms from those of the Hamilton group. 



Formation and localities. In the lower portion of the Chemung group, at 

 Ithaca and Cortland, N. Y. 



MODIOMORPHA AFFINIS, n. sp. 

 PL.VTE XXXVII, FIGS. IS, U ; AND PLATK XXXV, FIG. 13 



Mudimnorpha alta, in part {Coskkd), Hall. Pal. N. Y., vol. v. pi. 1. Platf.s mul Kxplanations: PI. 37, 



figs. 13, 14. 1883 



Shell large, robust, obliquely ovate, arcuate ; length about one-third greater 

 than the height ; basal margin straight or slightly arcuate, curving rather 



