WHiTEAVES.] FOSSILS OF TEIA.SSIC ROCKS OF BRITISH COLUMBIA. 135 



both of which are probably referable to the present species. The first 

 of these (fig. 6) is a small piece of rock, upon one of whose surfaces 

 a well-preserved cast of the interior of the basal portion of a left valve 

 and a similar cast of a right valve, with the anterior margin broken 

 off, are exposed to view. In this specimen the right valve is conspic- 

 uously flatter than the left, and the height of both is obviously greater 

 than their maximum length. The second, which is most likely only a 

 transversely elongated form of the species, is a nearly perfect but not 

 very well-preserved cast of the interior of the left valve. This diflei's 

 from the type specimen in being much more distinctly inequilateral, 

 in being a .ittle longer than high, in its more broadly rounded pallial 

 border, and in the circumstance that its anterior cardinal angle is 

 more rounded. Should the whole of these specimens prove to belong 

 to the same species, the original diagnosis of the characters of the latter 

 will, of course, have to be considerably modified, but in the meantime 

 it is thought most prudent to select the most perfect example collected 

 as the type, and to describe it first without reference to any of the 

 others. 



TriGONODUS (?) PRODUCTUS. (N. Sp.) 

 Plate 17, figs. 7, 7a and 7 b. 



Shell small and slightly compressed at the sides, the maximum 

 thickness through the closed valves being a little less than their great- 

 est height, very inequilateral, longer than high and narrowly subovate 

 in marginal outline, valves closed all round, not gaping at either extre- 

 mity. Anterior side short and regularly rounded at its margin : pos- 

 terior side much longer and narrowing gradually to a point which is 

 more or less obtuse in diffei-ent specimens, some of which are more 

 elongated and more narrowly pointed behind than others : ventral 

 margin gently convex, most prominent in or a little in advance of the 

 middle, rounding upwards rather abruptly in front and somewhat 

 straighter behind : superior border sloping gradually downward behind 

 the beaks and very rapidly so in front of them : umbones broad and 

 projecting very little, if at all, above the highest level of the cardinal 

 border: beaks small, depressed, curved inward, downward and for- 

 ward, and placed near the anterior end : escutcheon or ligamental area 

 (?) lanceolate and tolerably well-defined : lunule none. 



Surface marked by numerous concentric and impressed lines of 

 growth, most of which are not visible without the use of a lens. Test 

 apparently thin. Characters of the interior of both valves unknown. 



Dimensions of one of the specimens figured (a right valve) : maxi- 



