360 



to tbe 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 ante- 

 riorly, where it is distinctly concave on each side of the carina formed 

 by the erect dorsal margins of the valves, bordered along each side by 

 a low ridge commencing very narrow at the beaks and widening 

 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 costse, extending 

 up to the dorsal margin; beaks nearly terminal, rather narrow, erect, and 

 strongly incurve i at nearly right angles to the longitudinal axis of the 

 valves. Surface ornamented by from eighteen to about twenty-two angu- 

 lar transverse costfe that terminate abruptly above, along the low ridge 

 bounding the escutcheon ; costfc sometimes slightly crenated, particu- 

 larly those on the more gibbous anterior region ; lines of growth moder- 

 ately distinct. Internal cast showing only obscure traces of the costee; 

 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 costse, this shell 

 resembles T. limhata, d'Orbigny (Paleont. Fr. Terr. Cret., iii, pi. 298). 

 It may be readily distinguished, however, not only by its less promi- 

 nently-rounded anterior ventral region and more erect and more ante- 

 rior 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 costie do not pass. In the latter char- 

 acter, it agrees more nearly with T. crenulata, Lamarck, and T. aliformis, 

 Parkinson ; but it differs from these species too decidedly in form and 

 the nature of its costse to require detailed comparisons. 



It is almost certainly the same shell that was referred by Mr. Ether- 

 idge among3Ir. Hector's collections from iTanaimo, to T. IJmoryi, Con- 

 rad (pi. iii, fig. 2, a, b, c, United States and Mexican Boundary Survey 

 Eeport). It is, however, certainly very distinct from that species, not only 

 in form and in its decidedly less creuate costte, but more particularly in 

 having a smooth, longitudinally sulcate, depressed ridge along each side 

 of its escutcheon, not crossed by the costai. Its costte are likewise less 

 numerous and more prominent. 



Locality and position. — Cretaceous beds at Nanaimo, Yaacouver's Isl- 

 and. 



Mr. Gabb states, in the California report, that it is common in divis- 

 ion A of the survey of that State, at Tuscan Springs, Tehama County; 

 Chico Creek, Butte County; Curry's, south of Mount Diablo; Benicia; 

 Martinez; Eancho de 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 River, 

 Oregon, containing beautiful, sharply-defined moulds of this species. 



Genus PEOTOCARDIA, Beyricli. 

 Protocaedia scitula Meek. 



Plate 3, figs. 4 and 4 a. 

 Cardiwm scitidutn, Meek (1857), Trans. Albany Institute, iv, 40. 



Shell very small, circular or subquadrate, gibbous ; anterior margin 

 rounded ; posterior side subtruncated ; base slightly rounded ; beaks 

 nearly central, gibbous, incurved, and moderately elevated ; surface 



