| OCR Text |
Show 360 to the beaks; posterior extremity quite narrowly rounded, or subtruu cated; dorsal margin very concave in outline, and sharply carinate or erect along its whole length; escutcheon lance- oval, being widest anteriorly, where it is distinctly concave on each side of the carina formed by the ereot dorsal margins of the valves, bordered along each side by a low ridge commencing very narrow at the be^ ks and wideniug gradually posteriorly, with a well- defined narrow mesial sulcus along the entire length of each of these ridges; concave space within these ridges ornamented by small, nearly smooth, transverse cost ® , extending up to the dorsal margin; beaks nearly terminal, rather narrow, erect, and strongly incurved at nearly right angles to the longitudinal axis of the valves. Surface ornamented by from eighteen to about twenty- two angular transverse costte that terminate abruptly above, along the low ridge bounding the escutcheon; cost ® sometimes slightly crenated, particularly those on the more gibbous anterior region; lines of growth moderately distinct. Internal cast showing only obscure traces of the costs; posterior muscular impression deep; pallial line moderately distinct Length, 2.65 inches; height, about 1.86 inches; convexity, 1.70 inches. In its general outline as well as in the nature of its costoe, this shell resembles T. limbata, d'Orbigny ( Pahkmt. Fr. Terr. Cr6t., iii, pi. 298). It may be readily distinguished, however, not only by its less prominently- rounded anterior ventral region and more erect and more anterior beaks, but by its more arcuate dorsal outline, and especially by having along each side of its escutcheon a depressed, longitudinally* sulcated ridge, upon which the costse do not pass. In the latter character, it agrees more nearly with T. crenulata, Lamarck, and T. aliformit, Parkinson; but it differs from these species too decidedly in form and the nature of its cost& to require detailed comparisons. • It is almost certainly the same shell that was referred bv Mr. Ether-idge among Mr. Hector's collections from Nanaimo, to T. Emoryi^ Conrad ( pi. iii, fig. 2, a, ft, c, United States and Mexican Boundary Survey Beport). It is, however, certainly very distinct from that species, not only in form and in its decidedly less crenate costse, but more particularly in having a smooth, longitudinally sulcate, depressed ridge along each side of its escutcheon, not crossed by the costse. Its costoe are likewise less numerous and more prominent. Locality and position.- Cretaceous beds at Nanaimo, Vancouver's Island. Mr. Gabb states, in the California report, that it is common in division A of the survey of that State, at Tuscan Springs, Tehama County; Chioo Creek, Butte County; Curry's, south of Mount Diablo; Benicia; Martinez; Banchode San Luis Gonzaga, Pacheco's Pass; Jacksonville and Siskiyou Mountains, Oregon. Mr. William P. Blake also presented to the Smithsonian Institution some masses of rock from Crooked Hirer, Oregon, containing beautiful, sharply- defined moulds of this species. Genus PROTOCARDIA, Bevrich. PROTOCARDIA SOITULA Meek. Plate 3, figs. 4 and 4 a. Cardium scitulum, Meek ( 1857), Trans. Albany Institute, iv, 40. Shell very small, circular or subquadrate, gibbous; anterior margin rounded; posterior side subtrunoated; base slightly rounded; beaks nearly central, gibbous, incurved, and moderately elevated; surface |
