55 



to by Dr. Dall, but the unusually perfect specimen represented on Plate 

 10, which was collected at Durham by Mr. J. Townsend in 1884, is 

 probably the pedicle valve of a variety of T. Ohioensis. The interior 

 of this valve, however, is so completely filled with the matrix that its 

 identity with that species is not quite certain. The exterior of the 

 valve is compressed convex, its marginal outline broadly subovate, 

 broader t\mn. long and broadest in advance of the midlength. The beak 

 is slender, elongate and acuminate, its apex being acutely pointed and 

 slightly incurved. The maximum length of the valve is a little more 

 than three inches, and its greatest breadth not quite two inches and a 

 half. Its outer service is marked with concentric striae of growth. Its 

 " deltidium " is much higher or longer than broad, but the surface 

 markings of the whole of its cardinal area are obscured by the tough 

 and tenacious matrix. 



A cast of the interior of both valves of a specimen from Elora, kindly 

 lent to the writer, for examination, by Mr. B. E. Walker, of Toronto, 

 appears to be referable to this species. 



In the second part of the first volume of the " Report of the Geological 

 Survey of Ohio," pages island 185, Mr. Meek concludes that T. Ohioensis 

 is more nearly related to T. acuminata than to T. grandis, and states that 

 he " should not be surprised if further comparisons should prove the T. 

 Ohioensis to be only a more robust, broader variety of T. acuminata." 



Trimerella Billingsii, Dall. 



Trimerella Billingsi, Dall 1871. Am. Journ. Conch., vol. VIII., 



pt. 2, p. 82, pi. 11, figs. 1 and 2, but, 

 ace. to Dav. & King, not fig. 3. 

 " " Davidson & King,. 1874. Quart. Journ. Geol. Soc. Lond. , 



vol. XXX., p. 150, pi. 16. figs. 8 and 9. 



" One cast of a neural valve showing the characters of the area, pos- 

 terior margin, &c., distinctly, was kindly lefit for examination and 

 description by Mr. Billings. I have also seen two other specimens from 

 the same locality." Dall. 



"All we have seen of this species is the internal cast, measuring two 

 inches three lines in length by one inch five lines in width, of a single 

 pedicle-valve, found by Mr. Billings in the Guelph limestone at New 

 Hope, West Canada." Davidson and King. 



The cast of the interior of the pedicle valve referred to in the foregoing 

 quotations, which was collected by Mr. Billings at Hespeler in 1857, and 

 which is still in the Museum of the Survey, is the only specimen of T. 

 Billingsii that the present writer has seen. 



