SPIRIFERiE OF THE UPPER HELDERBERG GROUP. 
209 
distance from the beak. Fine close concentric undulating striae mark 
the entire surface. 
This shell may be distinguished from the last, as well as from other somewhat 
allied forms, b}^ its larger and more anguM* as well as less numerous plications, 
and in having a distinct linear ridge along the margin of the area of the ventral 
valve : its foramen is likewise narrower, and the sinus deeper and more angular 
than in S. segmenta. 
The individuals observed are too few to determine what changes may supervene 
from age and surrounding conditions ; but with our present knowledge, it cannot 
be united with any other similar form described. 
Figures 9 and 10, Plate 31, are illustrations of the original specimen described. 
Geological formation and localities. In limestone of the age of the Upper Hel- 
derberg group, at Stafford, Genesee county ; and at Shortsville, Ontario county, 
New-York. 
Spirifera ciiruteines. 
PLATE XXXI. 
Delthyris ( Spirifer ) euruteines : Owen, in Report of Geological Explorations in Iowa, Wisconsin and 
Illinois for 1859,* p. 74, f. 9, Plate 12. 
Spirifer euruteines : Owen, Geological Survey of Wisconsin, Iowa and Minnesota, p. 586,Tab.iii (exclu¬ 
ding figures 2 and 2 a), figures 6, 6 a, b. 
Shell semielliptical; length and breadth about as six to ten : hinge-line 
equal to the greatest width of the shell. Surface plicate. 
Ventral valve subpyramidal, the elevation being nearly equal to half 
the width, curving abruptly and equally to the front and lateral mar¬ 
gins ; the distance from the apex to the cardinal extremity and to the 
front of the shell being about equal. Apex sometimes projecting slightly 
over the area : mesial sinus shallow, well defined, and reaching to the 
apex, sometimes a little flattened in the bottom. Area extremely ele¬ 
vated, nearly flat or slightly concave above; fissure large and open 
to the apex, the length of the sides being about once and a half the 
width at the base. 
“ * Report of a Geological Exploration of Part of Iowa, Wisconsin and Illinois, made under instructions 
from the Secretary of the Treasury of the United States in the autumn of 1839 ; with charts and illus¬ 
trations. By David Dale Owen, M. D., Principal Agent to explore the mineral lands of the United 
States. Ordered to be printed, by the Senate of the United States, June 11, 1844.” 
[ Paleontology IV.] 27 
