284 
PALAEONTOLOGY OF NEW YORK. 
A medium-sized specimen lias a length of 38 mm., and a height of 23 
mm. A large individual measures 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 angular umbonal ridge, more direct 
truncation of the posterior end, and the obsolescence of the strise 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. 
Modiomorpha rigina, in part, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 41, fig's. 10, 
11. 1SS3. 
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. 
PLATE XXXVII, FIGS. 13, 14; 'AND PLATE XXXV, FIG. 13. 
Modiomorpha alta, in part (Conrad), Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: 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 
