liRACmOFODA. 45 



(a species then known only lioin an imperfect interior of the brachial valve), as 

 was subsequently done by Davidson and King, Dall, and Whiteavks, but it was 

 simply suggested that Billings' species might prove a representative of the 

 same genus. 



Mr. WiiiTEAVES lias given {loc. cil.) lignves oi' Rhinobolus Galknsis, which repre- 

 sent not only a brachial valve in entire agreement with the figures published 

 by Billings, Davidson and King, and with specimens in the possession of the 

 New York State Museum, but also a pedicle-valve, which is referred hy him to 

 the same species, but which does not at all agree with the original specimen of 

 KniNOBOLUS. It is, on the contrary, of about the same outline as the brachial 

 valve, with a low, incurved umbo and a very broad margin of contact, much 

 like that seen in the species Monomerclla ovata and M. Greenii. Should this 

 prove to be the pedicle-valve of the species, a doubt might fairly arise as to the 

 propriety of including it under the genus Rhinobolus. Mr. Whiteaves' speci- 

 mens are from Hespeler and Durham, Ontario, and all retain the shell, but it 

 does not appear that the valves have been found in connection. The original 

 specimen of Rhinobolus was from Gait, and before us is a very perfect 

 brachial valve from Elora, in exact agreement with those referred to Billings' 

 species, and this we are strongly disposed to consider as belonging to the same 

 form, on account of the complete harmony in the degree of development of the 

 platform and muscular scars. Our belief that these represent the same species 

 is further confirmed by specimens before us of a distinct species of the genus, 

 R. Davidsoni, sp. nov. (see Supplement), from the Niagara dolomites near Graf- 

 ton, Wisconsin, in which are found the same imperfect development of the plat- 

 forms, in association with a high cardinal area and erect beak. As already sug- 

 gested, the pedicle-valve referred by Whiteaves to R. Galtensis, resembles, as far as 

 it is known, certain Monomerellas, and it will be important to look for interiors 

 of this form which may lead to its correct allocation. Meanwhile Rhinobolus 

 Galtensis, Billings, may tentatively be regarded as the type-species of the genus. 



In regard to the generic characters of this species, the opinion liekl by 

 Davidson and King, that they represent an extreme aberrant variation of 



