5, Palap:ontographica Amkricaxa 64 



shell, which is of a rounded triangular form, with rather prominent prosocoelous beaks; 

 left valve with fine, elevated, rounded concentric lines, crossed by closer, less prominent, 

 and finer radial lines; in the right valve, as usual in this section of the genus, the radial 

 sculpture predominates over the concentric, the latter though present being inconspicu- 

 ous; cardinal area moderately wide, the beaks being nearly medial, the surface of the area 

 longitudinally striated; hinge with about five nearly vertical anterior teeth separated by 

 a wide unarmed gap from six or seven smaller, more oblique posterior teeth ; margin of 

 the valves thin, entire, or microscopically crenulated; the inner edges of the adductor 

 scars slightly raised above the inner surface of the valve * * '■-. It resembles A . pec- 

 tunculoides Scacchi and A. glomerida Dall, of the recent fauna, but is smaller, more in- 

 flated, and more triangular than either of them." 



Scapharca {Bathyarcd) Spenceri Yi3X^\ Plate X\'I, Figures 2, 3; (Dall, Wagner Free 

 Inst. Sci., Trans., vol. 3, p. 652, pi. 32, figs. 16, 24, i8g8), from the Pliocene of Tehuan- 

 tepec, is large for the section, (18 mm. long), "inflated, ovate, with prominent prosocoe- 

 lous beaks; left valve with fine, rounded, concentric elevated lines, close set, and with 

 verv narrow interspaces, which show fine, close radial striae, some of which on the an- 

 terior end of the shell are more prominent; right valve with fine, close-set radial ribs, 

 coarser on the middle of the shell, separated b}' narrower, sharp, channelled grooves; 

 transverse sculpture of evenh' spaced, low, sharp elevated lines which cross the ribs with- 

 out becoming much thickened; cardinal area ver>^ narrow behind, wider but not distinctly 

 limited in front, the cardinal margin elevated anteriorly, with seven or eight concentric 

 grooves mostly behind the umbones; ends of the hinge angular behind; the teeth in two 

 series hardly separated, eight to twelve in front, ten to fourteen behind, not crowded, 

 smaller mesialty, larger and more obUque distallj', the anterior series somewhat irregular; 

 inner margin of the valves with fine crenulations, stronger in the left valve, the outer 

 edge almost or quite entire. 



Scapharca i^Bathyarca) glomerula Dall; Plate XVI, Figures 4, 5; {Dall, Bull. Mus. 

 Comp. Zool. Han-^ard, vol. 9, p. 121, 18S1; vol. 12, p. 241, pi. 8, figs. 9, ga, 1886; U. S. 

 Nat. Mus., Bull. 37, p. 42, pi. 8, figs. 9, 9a, 1889; Wagner Free Inst. Sci., Trans., vol. 

 3, p. 659, 1898), recent from Hatteras to St. Vincent in one hundred to six hundred and 

 eighty-three fathoms, is similar in general shape, size and sculpture to A. pectiaicidoidcs, 

 but is shorter and higher; the hinge is straight with from fifteen to seventeen stout nearly 

 vertical teeth, usually in a continuous series, those at the ends of the series oblique; the 

 sculpture of the two valves is different, the radiating sculpture stronger on the right 

 valve; the radiating sculpture appears inside the shell within the margin in a series of 

 small ridges, generally with the same level as the rest of the interior, but sometimes ris- 

 ing into little tubercles, and separated by rather deep, short, narrow depressions, which 

 do not extend far inward nor over the smooth margin. The dimensions of A. glomeruia 

 are: Ion. 5.75, alt. S-o, diam. 5.0; Ion of hinge-line, 4.25 mm. Dall places Area {Scaph- 

 arca?) inacqidsculpta E. A. Smith, (Challenger Rep. Lam., p. 267, pi. 17, figs. 8-8c, 

 1885), from deep water off Culebra Island, West Indies, in synonj^my with this species. 



Scapharca {Bafhyarca) pohryma Dall: Plate XVI, Figures 6. 7; (Dall, Bull. I\Ius. 



