208 PALEONTOLOGY OF NEW YORK. 



shell in both its young and immature conditions is, in a certain measure sug- 

 gestive of Rhynchotreta, a resemblance increased by the peculiar concentric 

 ornamentation of both, but lessened by the low, truncated beak of the pedicle- 

 valve of Cyclorhina. On the interior the structure is altogether different. 

 The shell presents a rare combination of structural features which have been 

 observed only in the single species mentioned. It seems to approach most 

 nearly to the type exemplified by Waaoen's genus Terebratoloidea, especially 

 in the structure of the deltidium and foramen. 



It is elsewhere observed that variations in the foramen and deltidial plates 

 among the rhynchonelloids were largely features of developmental value. In 

 this case, however, the great encroachment of the foramen on the substance of 

 the valve must have been fully effected at a very early stage of growth, for in 

 the youngest shells observed it is as extremely developed as in mature indi- 

 viduals. The alate or auriculate character of the cardinal extremities is a dis- 

 tinctive feature, while the slight development of the median septum and 

 cardinal process may not be regarded as of much significance in a comparison 

 with Terebratuloidea. The straightness of the crura is a feature quite un- 

 usual among the rhynchonelloids, perhaps nowhere so marked as here, while 

 the concave expansion of their extremities is of more frequent occurrence. 



Gends terebratuloidea, Waagen. 1883. 



1862. Rhynchonella, Davidson. Quarterly Journal Geol. Soc. London, vol. xviii, p. 29. 



1863. Rhynchonella, Db Koninck. Fossiles paleozoiques de I'lnde., p. 36. 



1883. Terebraiuloidta, Waagen. Salt- Range Fossils; Brachiopoda, pp. 413-424, pi. xxxiii, figs. 1-12. 



Diagnosis. " Shell more or less transversely oval or rounded, in its general 

 appearance Rhynchonelloid, with strongly plaited valves and a high median fold 

 in the dorsal and a corresponding sinus in the ventral valve. Hinge-line curved, 

 beak truncated with a terminal round foramen ; deltidium formed of two 

 distinct plates, which limit the foramen below only for a very short 

 distance. 



" Internally, the ventral valve with two strong hinge-teeth, which are, how- 

 ever, not supported by dental plates. The dorsal valve bears a tolerably large 

 triangular hinge-plate, which is united on both sides by the deep dental sockets. 



