382 Systematic Paleontology 



Occurrence. — Oriskany Fokmation, Kidgely Member. Cumberland. 

 CoUeclion. — IJ. S. National Museum. 



EENSSEL.liRIA MARYLANDICA Hall 



Plate LXVI, Figs. 18-24 



Renssehrria viarylandica Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 461, 



pi. cviii, figs. 3a-3m, 1861. 

 Rensselwria intermedia Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 463, pi. 



cviii, figs. 2a-2c, 1861. 

 Rensselwria marylandica Hall and Clarke, 1893, ibidem, vol. viii, pt. ii, p. 



258, pi. Ixxvi, figs. 8-20. 

 Rensselwria interm.edia Hall and Clarke, 1893, ibidem, vol. viii, pt. ii, pl. 



Ixxvii, figs. 26-28. 



Description. — " Shell elongato-ovoid, the outline elliptical-ovate, 

 broader above the middle and gently narrowing towards the front, which 

 is sometimes compressed; without mesial sinus or elevation. Ventral 

 valve ventricose, the greatest elevation at the first third from the beak, 

 where it is sometimes subobtusely angidar : beak small, incurved over the 

 opposite valve, and sometimes so much incurved as to close the foramen 

 partially or entirely ; often, however, showing the deltidial pieces : the 

 lateral margins, in old shells, abruptly inflected. Dorsal valve less convex 

 than the opposite, the greatest gibbosity being at the first third below the 

 beak, sometimes flattened towards the front and abruptly inflected at the 

 lateral margins; leaving, with the inllection of the opposite valve, a 

 flattened or concave space on each side. 



" Surface marked by fine radiating striae, which, in the silicified speci- 

 mens, are often scarcely distinguishable on the upper part of the shell. 



" The interior of the ventral valve shows a deep symmetrical cavity, 

 the muscular impressions occupying a narrow oval space above the middle 

 of the shell. The cardinal teeth are strong, and supported below by strong 

 dental plates, which, on their anterior edges, are separated from the side 

 of the shell, and, about halfway in the depth of the cavity, turn backwards 

 towards the beak, come together in the rostral cavity, and reach into the 

 foramen. From the anterior basal margins of these plates proceed the 



