PALEONTOLOGY OF NEW-YORK. 
Treiaaatospira costata (n.s.). 
Plate XXYIII A. Fig. 4 a - e. 
Shell transversely elliptical, length less than one-half the width : hinge 
line slightly declining on each side of the centre; cardinal extremities 
rounded : valves very moderately convex in the middle, and flattened 
towards the margins. Ventral valve with a well defined sinus below the 
middle : beak moderately elevated, incurved, and truncated by a small 
perforation. Dorsal valve convex in the middle, with a broad scarcely 
defined mesial fold; cardinal margin thin, and closely pressed to the 
opposite valve : beak incurved beneath the opposite, and filling a broad 
pit, leaving on each side an undefined false area on the ventral valve. 
Surface marked by simple radiating costre, about fourteen or fifteen ^or 
more) on each valve, three of which are elevated on the mesial fold 
and two in the dejoression; the entire surface granulose or punctate, 
the granules arranged in concentric lines with a few imbricating 
lamellse of growth. 
This species is well marked by its simple costse, which cover the mesial fold as 
well as the lateral portions of the shell. It is extremely extended laterally, and 
much appressed at the extremities and on the cardinal margins. Without careful 
examination, this species would readily be mistaken for a Spirifer with the area 
obliterated by pressure. 
Fig. 4 a, b. Dorsal and ventral valves. 
Fig. 4 c. Profile view. 
Fig. 4 cl. Front view. 
Fig. 4 e. Enlargement of the surface, showing the granulose punctate character, which is 
obscure from the silicification of the shell. 
Geological position and locality. In the slialy limestone of the Lower Heidelberg 
group : ILelderberg mountains. 
* 
