58 



Edge Mills, near Durham, J. Townsend, 1884 : a single specimen with 

 a considerable portion of the test preserved, though the apices of the 

 beaks of both of the valves are broken off. The specimen consists of two 

 pieces, which fit together exactly. One of these pieces, the original of 

 figure 1 on Plate 9, shows the test, though badly exfoliated, of the pedicle 

 valve, the well preserved hinge area of that valve, and an imperfect cast 

 of the interior of the brachial valve. The other piece shows both sides of 

 the test of the umbonal region and part of the beak of the brachial valve, 

 the other portion of that valve, as represented by figure 1 on Plate 15, 

 being drawn from a gutta percha impression of the corresponding cast of 

 the interior of the shell. The test in the umbonal region of the brachial 

 valve is fully half an inch in thickness. 



This remarkable shell is referred to the genus Monomerella, mainly on 

 the authority of Professor J. M. Clarke, who has carefully examined the 

 specimen described. The species differs from the typical forms of the genus, 

 in the enormous development of the beak and pedicle surface of the 

 brachial valve, and in the apparent presence of shallow platform vaults in 

 that valve, but it could very well be congeneric with such shells as M. 

 Egani and M. Kingii. 



Monomerella. Species uncertain. 



Rhynoholus Galtensis, Whiteaves. (Pars.). .1884. This volume, pt. 1, pi. 8, fig. 3a, 



but not fig. 3. 

 Monomerella, Sp. ? Hall & Clark 1892. Pal. N". York, vol. VIII., p. 45, 



pi. 40, figs. 3 and 4. 



The specimen from Hespeler represented on Plate 7, figure 3a, of the 

 first part of this volume, as the pedicle valve of Rhynoholus Galtensis, was 

 thus identified to a certain extent on the authority of the late Dr. Thomas 

 Davidson, by whom it had been examined and studied. Except in the 

 much greater proportionate breadth of the hinge plate, it is remarkably 

 similar, in shape, size and surface markings, to the brachial valve of that 

 species, but its interior is completely filled with the matrix. More recently, 

 however, Professors Hall and Clark have expressed the opinion that this 

 specimen is probably the brachial valve of a species of Monomerella, 

 and in this opinion the writer is inclined to concur. They state, with 

 much apparent justice, that this specimen does not agree with the pedicle 

 valve of the shell now known as Rhinoholus Galtensis, as figured by David- 

 son and King, but that " it is, on the contrary, of about the same outline 

 as the brachial valve " of that species, with a low incurved umbo and a 

 very broad margin of contact, much like that seen in the species Mono- 

 merella ovata and M. Greenii." The brachial valve of M. ovata, however, is 

 much larger, more strongly convex, and its beak much more incurved than 



