80 PALAEONTOLOGY. 



very faint traces of a few .similar costaj are sometimes seen on each side of 

 the sinus. Surface of both valves marked by fine lines, and more or less 

 stronger sulcations of growth, which undulate gracefully in crossing the 

 costa?. 



Length, 1 inch; breadth, 0.9.3 inch; convexity mdcnown. One pro- 

 portionally broader specimen measures 0.!)3 inch in length and LOG inches 

 in breadth. 



The specimens of this shell in the collections studied by me are merely 

 distorted casts with portions of the shell attached. These so nearly resem- 

 ble Lciorhi/nchus muUicostatus, Hall (supposed by Trofessor Hall to be prob- 

 ably only a variety of L. quadricostafus, Vanuxem, sp., from the Hamilton 

 Group, N. Y.), that I had called attention to the close similarity. On com- 

 parison, however, with the figures and descriptions of the N. Y. shell, I 

 thought them most proljably distinct, and had proposed, in manuscript, a 

 new name for them. Since then Professor Hall and Mr. Whitfield, who 

 have investigated Mr. King's later collections, have referred this shell to L. 

 quadricostatus, Vanuxem (see Am. Jour. Sci, XI, 475, June, 1875). As 

 they have had the advantage of making direct comparisons with authentic 

 New York specimens of Vanuxem's species, which I had no opportunity to 

 do, it is presumable that they are more apt to be coirect. Consequently, as 

 these pages are passing through the press, I have withdrawn my proposed 

 name; and, as it has never been published with a description, it need not be 

 cited in synonymy. 



The group LeiorJii/nchus seems to be, so far as yet known, distinguished 

 from the older types of RhynclioneUa more by the obscurity and obsolescent 

 character of its plications, and other superficial characters, than by any 

 observed fundamental diff"erences of the muscular or other internal peculiar- 

 ities. The known New York species are found only in the Hamilton and 

 Chemung Groups of the Devonian. 



Locality cmd position. — White Pine Mountains, Nevada; where it occurs 

 in a dark shale. If a true Leiorhi/nchus, and especially if identical specifically 

 with the New York shell referred to, the black shale from which it was 

 obtained, would be almost certainly, as I had suspected, Devonian, and not 

 Carboniferous. 



