187 



points in which T. crassula resemliles tlie present speciee. The moat 

 noticeable of these are, first, that both have two furrows or grooves, 

 which, to use Stoliczlca's words, " run along the greatest convexity from 

 near the apex to the ])eriphery," and, secondly, that the anterior auricle of 

 both is minutely sti-iated. But, on the other hand, the striae on the 

 posterior auricle of T. crassula are stated to be finer than those on the 

 median area, the opposite being the case in T, Suciensis, and further, if 

 Stoliczka's figure be correct, which there is no reason to doubt, the 

 height of the valves of T. crassula is greater than their length, wherea8 

 in T. Suciensis the shell is certainly longer than high. 



Martesia clausa, Gabb. 

 Plate 17, figures 2, 2a and 26. 

 Martesia clausa, Gabb.— Pal. Cal., Vol. I., p. 145, pi. 22, fig. 115. 



Productive Coal Measures, Division A, of Noi-th West Bay, Y. I. : 

 J. Richardson, 1871. Several very perfect specimens boring into fossil 

 wood. 



The Vancouver Island variety of Martesia clausa is more elongated 

 than the type of the species figured in the " Palaontolog}^ of California," 

 and its double umbonal groove is much narrower. The umbonal 

 groove of the Californian shell is said to widen rather rapidl}^ below, but 

 in Mr Richardson's specimens there is an exceedingly narrow, linear, 

 flattened ridge, scai'cely any wider at the ventral margin than near the 

 beaks, with a shallow groove on each side of it. The calcareous filling 

 up of the anterior gap. or foot opening, appears to be divided in a line 

 with the opening of the valves ; it is much swollen and projects some- 

 what beyond the front margin of the valves. The umbonal accessory 

 valve or plate is preserved in two of the specimens from North West 

 Bay: its outline is broadly oval, the width being greater than the length, 

 and in front, between the beaks, it is developed into a small rounded 

 lobe. Along its centre there is a longitudinal line, which divides the 

 plate into two nearly equal portions, but the dividing line is a little 

 sinuous posteriorly, and may possibly have been caused by an accidental 

 fracture. It cannot at present be positively stated that the umbonal 

 valve or plate is divided longitudinally in its normal state, but if such 

 should prove to be the case the species would agree better with the 

 definition of Farapholas that with that of Martesia. Stoliczka, however, 

 says that the distinction between these genera, which is based principally 

 on the division or non-division of the umbonal plate, " scarcely deserves 



