Marylaxd Geological Survey 377 



Genus RHYNCHONELLA Fischer 

 EhYXCHOXELLA ( ?) BIALVEATA Hall 



Plate LXVI, Fig. 4 



lihynchonella ? Malveata Hall, 1S57, Tenth Ann. Kept. N. Y. State Cab. Nat. 



Hist., p. 73. 

 Khynchonella ? bialveata Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 233, pi. 



xxxiv, figs. 1-4, 1861. 

 RhyncJionella ? Malvcata Weller, 1903, Geol. Surv. N. J., Pal., vol. iii, p. 327, 



pi. xlii, figs. 9, 10. 



Description. — " Shell small, triangular or triangular-ovate, sometimes 

 compressed : valves nearly equally convex ; beak of dorsal valve incurved ; 

 beak of ventral valve almost straight and subangular; foramen narrow tri- 

 angular, and continued to the apex of the beak. Surface ornamented by 

 from twelve to fourteen simple angular plications on each valve; the two 

 central of which, on the dorsal valve, die out a little before reaching the 

 beak, near which they are somewhat depressed, but towards the front they 

 become slightly elevated above the others, so as to form an indistinct mesial 

 prominence: the middle plication on the ventral valve is smaller than the 

 others, and depressed near the front so as to produce a faint sinus, which 

 extends about two-thirds of the way to the beak, at which point the valve 

 is most convex: the two plications bordering the sinus are larger and 

 more prominent than those on each side of them, and become obsolete 

 before reaching the beak. A few faint imbricating lines of growth are 

 visible near the junction of the valves in front." Hall, 1857. 



Length 4.5 mm. ; width 3.75 mm. 



This specimen is more transverse and shorter than is usual for the 

 species, but it has all the other characters, including the two medial pli- 

 cations that arise in a sinus and make the narrow anterior dorsal fold. 

 Weller found this species in the Lower Oriskany of New Jersey. 



Occurrence. — Helderberg Formation, New Scotland Member. 

 Corriganville. 



Collection. — George M. Eoeder. 



