a08 PALEONTOLOGY OF NEW-YORK. 



The condition of the specimens is such as not to admit of satisfactory investigations 

 of the interior, whicli must for tlie present remain partially undetermined. 



The siMJcies positively determined to the present time are from the rocks of the 

 Lower llelderberg group; to which mjiy be added the Tremafosjyira {Jltryj)a) camura 

 of the Niagara group, which presents some slight deviation in the perforation of the 

 l>eak. 



Treniatospira perforata ( n. s.). 



Plate XXVIII A. Fia. 3 a - i. 

 Spiryftri perforaiita : Hall, Desc. of Now Species of Pal. Fossils, in Regents' Report for 1856. 



Shell somewhat semicircular on the ventral side, with the hinge ex- 

 tremities rounded ; hinge line slightly curved : valves nearly equally 

 convex. Ventral valve rhomboidal, with a broad subangular sinus : 

 beak elevated, incurved and truncate at the extremities by a distinct 

 round perforation ; a broad triangular pit or foramen beneath the beak. 

 Dorsal valve with beak strongly incurved, and filling the foramen of 

 the opposite valve. 



Surface marked by sharp radiating striae, which bifurcate once or twice 

 before reaching the base, presenting fascicles of two or three on the 

 centre of the shell. 



This species has the general aspect of Rhynchonella ; but the strise are fascicu- 

 late, and the cardinal line more extended. In the perforate beak of the ventral 

 valve, the broad foramen filled with the beak of the dorsal valve, and the internal 

 spires, it resembles the T. multistriata, but differs from it in the fasciculate strise, 

 and in the more elevated and less strongly incurved beak of the ventral valve. 

 The sinus varies from a shallow scarcely defined depression in the young, to a 

 strongly marked angular feature in the older shells. 



Fig. 3 a. Dorsal view of a small specimen. 



Fig. 3 b, c, d. Dorsal, ventral, and profile views. 



Fig. 3 e, f. Dorsal and ventral views of an older specimen with deep sinus. 



Fig. 3 g, A. Front views of a young and old specimen, showing the shallow and deeper 

 mesial sinus. 



Fig. 3 i. Ventral side of an imperfect specimen, showing the internal spire. 



Fig. 3 k. Enlargement showing perforated beak and junction of the valves. 



Geological position and locality. In the shaly limestone of the Lower Heldcrberg 

 group : Helderberg mountains ; and Becraft's mountains, Hudson. 



