198 . 
PALAEONTOLOGY OF NEW-YORK. 
This species bears some analogy to the L. transversalis of the Niagara group, but 
is proportionally shorter on the hinge line, ancl 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 views. Fig. 2 c. Profile view. Fig. 2. Enlargement of area, foramen, etc. 
Geological position and locality. In the slialy limestone of the Lower Helderberg 
group : Helderberg mountains, Albany county. 
Spirifer vaiiuxemi. 
Plate VIII. Fig. 17 - 23. 
Orthis plicata : Vanuxem, Geol. Report Third District New-York, 1843, pa. 112, f. 1. 
Not Spirifer plicatus of Sowerby, of Hoen, or of Steininger. 
Shell rhomboidal, moderately gibbous : extremities 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 strife and stronger imbricating lines of growth, 
'which are again crossed by still finer radiating strife ; 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 group have a smaller area and 
less elevated beak of the ventral valve, as well as a less gibbous form. The concen¬ 
tric strife are more rounded and much more interrupted by inequalities of surface 
from laminae of growth, while the fine longitudinal strife are stronger and more 
continuous. 
The S. vanuxemi 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 striae 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. 
