LAMELLIBEANCHIATA OF THE LOWER MARLS. 59 



pecially of his B. striata, given in the Min. Conch., and it is equally cer- 

 tain that the shells are perfect and without injury; and the lines of growth 

 clear, clean, and distinct as on any living shell. The triangular foramen 

 extends from the beak forward to the position of the hinge-line, and later- 

 ally to the entire width of the shell at this point on both sides, leaving the 

 entire cardinal portion of the shell forming a single broad triangular open- 

 ing in each valve, while the margins are elevated and sharp, with the lines 

 of growth passing over them in perfect continuity. What the purposes of 

 this opening may have been I cannot say. It is not the position for a 

 byssus, or any organ of similar nature; nor can it have been needed for 

 any analogous purpose, as the shells are all, so far as I have seen, firmly 

 anchored or attached to foreign substances. The small specimen figured 

 was attached only by the beak, but that by a surface nearly or quite a 

 fourth of an inch wide. From the form of the apex of the upper valve, as 

 far as I have seen them, I judge it curved over this opening in such a 

 manner as to partially cover it, as they are all extremely ventricose in this 

 part. But this was not the case in the English species, for there the upper 

 valve is but moderately convex. So the question as to the purpose of the 

 opening remains unsolved. 



Dianchora ecbinata. 

 Plate X, Figs. 3-9. 



Plagiostoma ecUinatum, Morton. Synopsis, additional observations, § iv. 



Spondyltis ecUinatum (Mort.) Meeli, Check-list, p. 71. Geol. Surv. K. J., 18G8, p. 72-1. 



8. capax Conrad. J. A. N. S., Phil., 2d ser., Vol. II, p. 274, PI. XXIV, Fig. 8. 



Shell below medium size, subcircular or very broad-ovate in general 

 outline, and with a very highly convex or gibbous free valve. Lower 

 valve fixed to foreign substances, and often by nearly its entire surface, and 

 conforming in depth to the surface to which it is affixed, or nearly so. Or 

 when more concave the space between the margin of the shell and tlie object 

 to which it is attached is filled up with shelly matter formed in the same 

 manner as the spines of the valves. The cardinal portion of the valve is 

 open, forming a bi'oad triangular foramen the entire width of the valve at 

 this point, the margins of the foramen being sharp, no hinge-teeth or cardi- 



