43 American East Coast Arcas 43 



Ocaincnce. — Miocene of North Carolina? Wagner; of York River, Virginia, station 

 2250; of Duplin County, North Carolina (young). — Dull. Miocene of North Carolina. — 

 C. U. Museum. 



Area callicestosa Dall 

 Plate X, Figures 3,4,5 



Scnpharca [Scapkarca) callicestosa Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 638, pi. 34, 

 figs. 17, i8, 1S98. 



"Shell of moderate size, rather thin, rhomboid al, with small, prominent, mediosul- 

 catc, prosocoelous beaks situated at about the anterior third of its length; left valve with 

 about thirty-seven squarish subequal radial ribs, separated by narrower channelled inter- 

 spaces; on the tops of these ribs are four longitudinal threads, the inner pair larger and 

 more prominent but separated by a somewhat deeper sulcus than those external to the 

 inner threads; concentric sculpture of fine, close, rounded, slightly elevated threads, 

 which overrun the whole shell, ribs, and interspaces, and at short intervals, at the inter- 

 section with the inner pair of rib-threads, they become minutely nodulous, while the 

 reticulations have a punctate ajjpearance, giving a surface somewhat like fine lace and 

 peculiar, as far as obser-ved, to this species; cardinal area short, rather narrow, with 

 sharply elevated boundaries and a single incised set of grooves forming a lozenge-shaped 

 figure anteriorly; hinge-line short, teeth in two adjacent series, anterior with fifteen, pos- 

 terior with twenty-six or twenty-seven teeth set vertically, a little oblique at the distal 

 ends of the series; each individual tooth more or less grooved or striate in the direction 

 of motion, as in some recent species; anterior end of shell produced, rounded; posterior 

 end subtruncate, base slightly arched; inner margin of the valves with rather long, deep 

 flutings, corresponding to the external ribs. L,on. 32, alt. 27, diam. 20 mm. (twice the 

 diameter of the single valve). 



"A single valve of this very elegant species was obtained by Mr. Burns. Its sculp- 

 ture differentiates it from all our other Tertiary species. Area callipleura Conrad, in 

 which the ribs have a minute nodular sculpture, has the radial threading predominant, 

 while in this species the concentric threads overrun all the rest. The two species are 

 entirely distinct otherwise." — Dall, 1898. 



The type specimen is not full-grown. About a dozen valves of this distinct species 

 are in the C. U. Museum. The adult shell has a somewhat more produced posterior end 

 and the cardinal area is wider with several grooves; there are often six riblets nearly 

 equal in size on each rib; besides the characteristic lace like reticulation the anterior ribs 

 usually show a coarser nodulation; on the right valve the ribs from the center of the shell 

 to the umbonal ridge are smoother as in Cunearca; ribs thirty-six to thirty. eight. 



A single left valve fossil from Nicaragua somewhat resembles this species in form and 

 markings. It is larger and more oblique, the young more inflated, the ribs narrower and 

 the fine reticulation, though present, is inconspicuous except near the umbonal ridge. 

 The shell is labelled Scapharca holoserica Reeve, but it is distinct from that species. 



Diniensiotis. — Lon. + 17,-33; alt. -(-5,-35; semidiam. 16 mm. 



