SPIEIFER^ OF THE UPPER HELDERBERG GROUP. 309 



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, by its larger and more angular 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 Ukewise narrower, and the sinus deeper and more angular 

 than in S. segmenta. 



The individuals observed are too few to determine what changes may superven® 

 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 euruteines. 



PLATE XXXI. 



DilthyrU (Spirifer) euruteines : Oweh, in Report o( Geological Explorations in Iowa, 'Wisconsin and 

 » Illiaois for 1859,* p. 74, f. 9, Plate 12. 



Spirifer euruteinei : Owkr, Geological Survey of Wisconsin, Iowa and Minnesota, p. 586,Tab.lii (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 (Jeological 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." 



[ PAL.S0NTOLOOY IV.] 27 



