NATURAL SCIENCES OP PHILADELPHIA. 117 







Missouri geologists to 0. Michelini (?). It is a small circular species, with 

 extremely fine ribs or strise, apparently too obscure for either 0. Michelini or 

 0. Vanuxemi. 



Orthis flava, n. sp. Shell small, transversely oval, slightly truncate on 

 the cardinal side. Ventral valve convex, perceptibly flattened toward the 

 anterior margin, though without a marked sinus ; most elevated near the 

 slightly projecting beak ; area rather high and broad, triangular, with an 

 equilaterally triangular foramen ; dental lamella? slender, short, diverging at 

 an angle of about 80 ; occlusor scars small, together enclosing a longitudinally 

 oval space, which readies one-third the distance from the beak to the anterior 

 margin ; a median internal ridge reaches froin the beak to beyond the middle 

 of the valve. The shell was evidently thin ; its surface marked by one hun- 

 dred or more delicate radiating ribs, which increase by implantation. 



Transverse diameter of shell -50 (100) ; longitudinal diameter -39 (78) ; 

 depth of ventral valve .12 (24). ~ 



Burlington, Iowa, apparently from Bed " No. 1." at the lbase of the yellow 

 sandstones. " White Collection," of the University of Michigan. 



This species is less circular than the forms referred to 0. Michelini, and has 

 a more convex ventral valve and larger area. It differs from 0. impressa, 

 Hall, (Geol. Rep. 11th Dist. N. Y., p. 267, fig. 2), in its more transverse 

 shape, smaller size, more convex ventral valve, and feebler sinus. 



Streptorhynchus lens? White, (Proc. Bos. Soc. Nat. Hist. ix. 28), /'Wey- 

 mouth, Medina County, Ohio, 80 feet below the conglomerate." Whittlesey's 

 Collection. 



Streptorhynchus umbraculum ? Schloth. sp. From "coarse bedded sand- 

 stone, next below conglomerate, Warren, Trumbull County, Ohio." Whittle- 

 sey's Collection. 



A large, undetermined species from oolitic limestone, "No. 6," Burlington, 

 Iowa, probably belongs here. Collected by A. Winchell. 



Streptorhynchus inequalis, White sp. From Weymouth, Medina County, 

 Ohio, 80 feet below conglomerate." Whittlesey's Collection. 



Streptorhynchus sp. ? A single interior of a ventral valve from 



"near Ashland, Ashland County, Ohio," resembles S. Chemungensis, var. 

 pectinacea, Hall. (Pal. N. Y., Vol. iv.) It differs, however, in the possession 

 of a longer hinge line, and distinct auriculations, and lacks the alternation in 

 the size of the radial ridges. 



Pentamerus lenticularis, White and Whitfield. This species, described 

 from the yellow sandstone of Burlington, occurs also in the base of the Bur- 

 lington limestone. " White Collection " of the University of Michigan. 



SPIRIGERA, D'Orbigny. 



Spirigera Missouriensis, n. sp. Shell of moderate size, broadly ovate, mo- 

 derately ventricose, with lamellose exterior. Ventral valve with an extended 

 beak, turned up at right angles with the plane of the shell, and having a cir- 

 cular perforation at its extremity. Between the beak and the dorsal valve is 

 an external flattening simulating an area, but traversed by the incremental 

 lines. Sinus a shallow but distinct groove, beginning at the beak, widening 

 and deepening anterior to the middle, and near the middle becoming well 

 characterized. Dorsal valve nearly circular, with straight hinge slopes, and 

 obtuse, beak closely incurved and concealed, though not in contact with the 

 ventral beak. Mesial fold less distinct than the sinus of the ventral valve, 

 arising near the middle of the valve. Both valves are marked by numerous 

 strongly imbricating lamella? of growth. Greatest thickness through the 

 middle of the ventral valve. 



1865.] 



