449 PALEONTOLOGY OF NEW- YORK. 



Itliynclioiiella burraiidi. 



Plate CIIL Fio. 3-8. 

 RhynchontUa harrandl : ITall, Regents' Report for 185G, p. 82; Palasozoic Fossils, 1857, p. 42. 



Shell very large, ovoid or subglobose ; full-grown specimens higher than 

 wide, vertically flattened on the sides. Dorsal valve very convex, often 

 extremely elevated : beak incurved ; cardinal border on each side of 

 the beak profoundly sinuate. Ventral valve much the smaller, strongly 

 arcuate longitudinally, having a broad shallow rounded sinus towards 

 the front, abruptly inflected at the lateral margins which are distinctly 

 angular, prolonged in front into a broad rounded linguiform projection 

 which fills the sinus in the opposite valve. 

 ScKFACE marked by thirty to forty simple (rarely bifurcating) strongly 

 elevated plications on each valve, as shown in casts of the interior : 

 plications rounded or subangular. 



This species has occurred only in casts, which are generally more or less distorted. 

 It is the largest of the genus known to me in the rocks of the country. The great 

 size, with the strongly marked internal characters which are impressed upon tlie 

 cast, will serve to distinguish this species from any other yet known. 



In many respects it resembles R. speciosa, which may be regarded as a representa- 

 tive form in the Maryland rocks : it is, however, distinguished from tliat shell by 

 its larger size, its more elevated dorsal valve and relatively broader form, and its 

 broad shallow rounded sinus near the front of the ventral valve. 



Fig. 3. Cast of the ventral valve, showing the large muscular impression. The area of the 

 adductor muscles is not represented as large as in the specimen. The depression 

 in front is less than one-eighth of an inch below the plane of the more prominent 

 margins. 



Fig. 4. A similar cast of a smaller individual, in which the form of the rostral cavity is 

 better preserved than in the preceding. The casts show a great thickening of the 

 shell at the beak. 



Fig. 5. Cardinal view of a specimen which is a cast from the interior of both valves, showing 

 the great elevation of the dorsal valve, the strong median septum, and the deep 

 sinuosity on each side of the beak. 



Fig. 6. Front view of the same specimen. 



Fiw. 7. Lateral view of the same, showing the great lateral extension of the dorsal valve. 



Fi". 8. Profile view of a cast of the ventral valve, showing the abrupt inflection at the 

 margin and the expansion of the shell below the beak, which fills the lateral 

 sinuosities in the opposite valve. 



Geological position and localities. In the Oriskany sandstone : Albany and Scho- 

 harie counties. 



