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 Waagen’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. 
Genus 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. Tei-ehratuloidta, 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. 
