I9§ PALJJONTOLOGY OF NEW-YORK. 



This species bears some analogy to the L. transversalis of the Niagara group, but 

 is proportionally shorter on the hinge line, and the area is much higher; the inter- 

 mediate striae are coarser, and the concentric wrinkles are not observed in the 

 species from the Niagara group. 

 Fig. 2 a, b. Ventral and dorsal riews. Fig. 2 e. Profile view. Fig. 2. Enlargement of area, foramen, etc. 



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

 group : Helderbei^ mountains, Albany county. 



Spirifer vana.\cnii. 



Plate VIII. Fio. 17 - 23. 



Orthit plicata : Vanuxem, Geol. Report Third District New-York, 1843, pa. 112, f. 1. 

 Not Spiri/er plicatus of Sowebbt, of IIokn, or of Steiningeh. 



Shell rhomboidal, moderately gibbous : ex^emities rounded. Ventral 

 valve the less convex, having the beak elevated and incurved. Area 

 small. 

 Surface marked by broad rounded or somewhat flattened and sometimes 

 undefined plications, of which there are from two to four on each side 

 of the mesial fold and sinus ; concentrically marked by fine closely 

 arranged undulating striae and stronger imbricating lines of growth, 

 which are again crossed by still finer radiating striae ; the latter visible 

 only under a magnifier. 



This species resembles very closely the S. crispus of the Niagara group ; but all 

 the specimens examined from the Lower Helderberg gi-oup have a smaller area and 

 less elevated beak of the ventral valve, as well as a less gibbous form. The concen- 

 tric striae are more rounded and much more interrupted by inequalities of surface 

 from laminae of growth, while the fine longitudinal strise are stronger and more 

 continuous. 



The S. vantixemi is extremely abundant in certain parts of the Tentaculite lime- 

 stone, and occurs in the base of the Pentamerus limestone. It differs from the S. 

 cyclopterus of the shaly limestone in its smaller size and less numerous plications, 

 as well as in the fine concentric and radiating strise of the surface. ; 



Fig. 17, 18 & 19. Young individuals of this species. 



Fig. 20 - 23. Dorsal, ventral, profile, and front views of several individuals. "' 

 Geological position and locality. In the Tentaculite limestone of the Lower Hel- 

 derberg group : Helderberg mountains, Albany county ; Schoharie, .^Carlisle, 

 Litchfield in Herkimer county, and other places. 



