357 



meoted by small linear radiating costiie, which are crossed by fine con- 

 centric striie and stronger marks of growth. I^fear the anterior end of 

 the shell, the radiating costic are a little larger and much more widely 

 separated than farther back. 



Length, 0.75 inch ; height, 0.47 inch ; breadth or convexity, 0.40 inch. 



I am not well enough acquainted with the hinge of this little shell to 

 be quite sure that it is congeneric with the form on vrhich I proposed to 

 found the genus Grammatodon in the Palteontology of the Upper Mis- 

 souri. One of the casts shows a little of the impression of the hinge in 

 front of the beaks, with apparently four or five small teeth, or denticles, 

 ranging obliquely forward and upward. The posterior muscular impres- 

 sion, as seen in this cast, shows no traces whatever of the lamina con- 

 nected with that of the posterior adductor, such as exists in Cuculkca. 



Localiiy and position. — Komooks, Yancouver's Island ; cretaceous. 



Genus? ARC A, Linn. 

 Aeca! equilatekalis, Meek. 



Plate 2, figs. 6 and 6 a. 

 Area {Cuculltea ?) e'^uilaieralis, Meek (lS57)j Trans. Albany Institute, iv, 40. 



Internal cast of medium size, equilateral, transversely oblong-oval 

 in form, gibbous in the central and umboual regions; anal margin 

 obliquely truncated ; anterior side subtruncated ; base nearly straight 

 along the middle, and rounding up abruptly at the extremities; dorsal 

 outline sloping from the beaks ; hinge less than the length of the valves, 

 and parallel to the base ; cardinal area comparatively small ; beaks 

 central, moderatelj^ elevated, and rather gibbous, but somewhat flat- 

 tened on the outside, and incurved at right angles to the hinge; muscu- 

 lar imi)ressions shallow. Surface (of cast) retaining faint traces of small 

 radiating costre, or strine. 



Length, 1.68 inches; height, 1.02 inches; breadth or convexity, 0.80 

 inch. 



This species will be readily distinguished from any other with which 

 I am acquainted, resembling it in other respects, by the central position 

 of its beaks. None of the specimens show the hinge, or surface-markings, 

 though, faint traces of radiating lines, or striiie, seen on the internal 

 casts, show that it was probably marked by small radiating costie. It 

 is not easy to decide from the specimens in the collection whether it is 

 an Area or a CucuUa'a, or, indeed, with certainty, whether it belongs 

 even to the Arcid(c. There is on the cast a shallow, obscure depression 

 near each posterior muscular scar ; but these depressions seem not so 

 distinct as those always seen on casts of Cuculkva, while none of the 

 specimens show the hinge, though there appears to be a small cardinal 

 area. 



LocaJitu and jJO'-'ition. — Xanaimo?, Vancouver's Island; Cretaceous."^ 



