293 



with the angular and subconcentric ribs or plications almost obsolete. A 

 little Triffonia, from the Cretaceous rocks on the south side of the en- 

 trance to Quatsino Sound, V.I., collected by Mr. Hunt of Alert Bay, and 

 lent to the writer by Dr. Newcombe, is probably a short, ventricose variety 

 of T. diversicostata. 



Arca (Nemodon) simillima. (N. Sp.) 



Nemodon Fischeri, Whiteaves. 1884. This volume, pt. 3, p. 23 1, pi. 31, fig. 5. But 

 probably not Arca Fischeri, d'Orbigny, 1850, which is a Russian 

 Jurassic species. 



Shell moderately convex, narrowly elongated, nearly three times as 

 long as high and very inequilateral. Anterior side short, anterior end 

 forming an angular junction with the cardinal border above, thence 

 curving abruptly and obliquely, inward and downward, to the ventral 

 margin below : posterior side fully four times as long as the anterior, 

 posterior end truncated somewhat obliquely and very shallowly concave 

 above, narrowly rounded and a little produced below : cardinal margin 

 straight and slightly ascending from the anterior to the posterior end : 

 umbones broad but not very prominent, placed at a short distance from 

 the anterior end : beaks rather widely separated, small and incurved : 

 cardinal area rather large, marked by continuous longitudinal grooves, 

 which are a little bent opposite the beaks : ventral margin shallowly con- 

 cave a little in advance of the midlength, narrowly rounded in front of 

 this sinus, much broader and nearly straight behind. 



Surface marked by very numerous, small, radiating ribs, and by con- 

 centric stri* and lines of growth. 



Hinge dentition apparently as in Nemodon (Conrad) and consisting of 

 three short, longitudinal, anterior teeth, parallel to the cardinal border, 

 with some granulous teeth opposite the beaks, and of two very long, 

 laminar posterior teeth, \#iich are also parallel to the cardinal border. 



East end of Maud Island, Dr. G. M. Dawson, 1878 : several well pre- 

 served and nearly perfect specimens. 



In a previous part of this volume these specimens were identified with 

 Arca Fiffcheri, d'Orbigny, on the strength of Eichwald's statement that 

 that species is from rocks of Neocomian age. These rocks are now 

 regarded as Jurassic, and although the figures of A. Fischeri* in the 

 second volume of the Geology of Russia in Europe and the Ural Moun- 

 tains are remarkably similar to the Maud Island specimens, it is scarcely 

 probable that a North American Cretaceous fossil is identical with a 

 Russian Jurassic species. 



* Under the name Arca concinna, von Buch, which D'Orbigny himself subsequently 

 changed to A. Fischeri. 

 31— M. F. 



