442 DESCRIPTIONS OF NEW SPECIES OF FOSSILS FKOM THE 



the shell. Horizontal lines of growth, without vertical cross lines, are conspicuously 

 developed on the cardinal area. 



On the ventral valve the muscular scars are strongly developed, and extend over 

 nearly two-thirds the length of the shell ; ovate in outline, the width being equal to 

 three-fourths of the length ; the area being largely occupied by the cardinals, between 

 which lie the narrow linear adductors. The casts of the dorsal valve show the marks 

 of the deeply striated cardinal process and elongate tooth-sockets. In casts of the 

 ventral valve the whole ujDiier portion and the area are marked by numerous irregu- 

 larly disposed prominent pustules. 



From the external characters alone it would be impossible to separate this species 

 from Spirifera disjuncta, but the intei"nal differences are generic. 



Formation and locality. Chemung group, near "Warren, Warren county ; and at 

 Union City, Erie county, Pennsylvania. 



MERISTELLA INCERTA Simpson, n. sp., Fig. 7. 



Shell subrhomboidal, greatest width at or a little below the middle ; length of 

 the ventral valve equal to the width; of the dorsal valve, slightly less. Yalves con- 



'fV^ 2' vex, the ventral valve being the most gibbous. An- 

 4 '>. tero-basal margins gently curving outward, at the 

 * , middle abruptly rounding and the front produced in 



■ '. ■ \ / a broad extension. 



APS. Trisas.^ Ventral valve the more convex; gi-eatest con- 



vexity a little above the middle, abruptly curving to the cardinal mnrgins, and more 

 gradually to the front. A comparatively deep, broad sinus extends from the beak to 

 the base, forming one of the most conspicuous features of the species. Umbo promi- 

 nent. The beak is broken away on the specimens observed, but enough remains to 

 show that it was rounded, closely incurved, nearly at right angles to the plane of the 

 axis. 



Dorsal valve less convex than the opposite, greatest convexity above the middle, 

 regularly curving to the antero-basal margins, elevated towards the base into a mesial 

 fold, which is much less conspicuous than the corresponding depression of the ventral 

 valve; beak small, incurved, lying below that of the opposite vah^e. 



The general aspect of the surface is tb.at of a smooth shell with a few strong 

 lines or varices of growth. There are indications of radiating stria?, and it is possi- 

 ble that specimens in a better condition of preservation would show both radiating 

 and concentric striie. 



