NATURAL SCIENCES OF PHILADELPHIA. 315 



A careful review of the subject, with the aid of the more extensive collections 

 brought in by the Boundary Survey, fully establishes the correctness of my 

 first suggestion in regard to the Cretaceous age of the doubtful beds at 

 Nanaimo. The species from the other rock referred at first to the Cretaceous, 

 although sent to the Smithsonian Institution mingled with others from 

 Nanaimo, are now known to be from Komooks, a locality some seventy miles 

 north-west of Nanaimo, on the eastern shore of Vancouver Island. 



Of these two Cretaceous formations, that at Nanaimo is apparently the older ; 

 while the deposits on Sucia Islands, (a small group in the Gulf of Georgia, 

 about seventy miles south-east of Nanaimo) belong to the same horizon as the 

 Komooks beds. 



Descriptions of Species. 



LAMELLIBRANCHIATA. 



Inoceramus subundatus Shell (left valve) broad ovoid or subcircular in 

 outline, rather compressed ; anterior margin rounding regularly from near the 

 beaks into the base, so as to form with the latter a semicircular curve ; pos- 

 terior side rather irregularly rounded, its most prominent part being near the 

 middle, hinge margin straight, equalling about half the entire length of the 

 shell ; and ranging at an angle of near 55 above the axis of the umbonal 

 prominence ; beak occupying a position nearly over the anterior margin, rather 

 small, and rising little above the hiuge. Surface ornamented by moderately 

 distinct, regular concentric folds, which are stronger on the most convex part 

 of the valve, and become nearly or quite absolute around the free borders. The 

 outer fibrous layer (which is exfoliated from the specimens examined) is, doubt- 

 less, marked also by concentric striae. 



Length, 3-45 inches; height, 2-94 inches; breadth or convexity about 0-75 

 inch. 



This species resembles /. Barabini of Morton, (specimens of which are con- 

 tained in the North-Western Boundary collections from Sucia Island in the 

 Gulf of Georgia.) It differs, however, in being more compressed than the corre- 

 sponding valve of that species. It is also much less regularly rounded pos- 

 teriorly, and the curve of its concentric folds is different. It may be dis- 

 tinguished from /. Vancouverensis of Shumard, by having its beak very much 

 less gibbous, and less prominent. 



Locality. Komooks, eastern shore of Vancouver Island. 



Dosisia? tenuis. Shell circular, or very slightly oval, extremely thin, and 

 much compressed; lateral and basal margins regularly rounded, and very thin 

 and sharp ; beaks small, compressed, central, and projecting little above the 

 dorsal margin ; lunule small and rather deep ; surface marked by fine concentric 

 stria?. 



Length and height each 1-26 inches ; convexity about, 0-22 inch. 



As neither the hinge, nor the interior of this species has been seen, it is only 

 referred provisionally to the genus Dosinia. It has much the appearance of a 

 Lucina, but casts of the anterior muscular scar visible on some specimens, show 

 these impressions to differ from those of Lucina. It seems to be closely allied 

 to Dosinia Icnticularis {Artemis lenticuhiris) of Forbes, from the Cretaceous at 

 Pondicherry, Southern India, (Trans. Geol. Soc. Lond. vol. vii. pi. 18, fig. 7.) 



Locality. Nanaimo, Vancouver Island. 



Mactra Gibbsana. Shell transversely oval, or subtrigonal, moderately con- 

 vex, rather thin ; anterior side narrowly rounded ; base forming a regular semi- 

 elliptical curve ; posterior side slightly truncated at the immediate extremity, 

 abruptly rounded or subangular at its connection with the base below ; dorsal 

 outline sloping from the beaks in front and behind, at an angle of about 120 ; 

 beaks central, rather elevated, but small, and not projecting much above the 



1861.] 



