OBOLID^. 569 



Type. — Oholella gemma Billings. Second species: Bicia wTiiteavesi Walcott. 



Observations. — Bicia is a form that conabines many of the characteristics of Oholella and 

 Oholus. It resembles Oholella in the arrangement of the muscle scars and main vascular sinuses 

 of the interior of the valves. It differs in having a high area with an open pedicle groove in 

 the ventral valve and an elevated ridge or boss in the back portion of the dorsal valve that 

 in one species, B. wTiiteavesi, is very prominent. The ensemble of the dorsal valve of Bicia 

 is unlike that of either Oholella or Oholus. Bicia with its thick shell, high area, deep central 

 cavity (heart-shaped cavity of Mickwitz [1896, p. 71]), arrangement of visceral cavity, muscle 

 scars, and vascular markings in the ventral valve, is a true Oholus of the 0. apollinis Eichwald 

 type; but in its more elongate outline, strongly striated surface, and in nearly all details of 

 the dorsal valve it is quite distinct. 



Of the two species now referred to the genus, B. gemma (Billings) has an unusually thick 

 shell and a very marked deposit of shell substance over the visceral area in the ventral valve, 

 the posterior portion of the same area in the dorsal valve, and along its median line. In the 

 second species there is a considerable deposit over the same area, with the exception of the 

 median line, where the strong median ridge is absent. 



The generic name is derived from the town of Bic, Quebec, near which the type species 

 was found. 



, Bicia gemma (Billings). 



Plate L, figures 1, la-n. 



Oholella gemma Billings, 1872, Canadian Naturalist, 2d ser., vol. 6, No. 2, pp. 218-219; fig. 5, p. 217. (Described 

 and discussed as a new species.) 



Oholella gemma Billings, 1872, Am. Jour. Sci., 3d ser., vol. 3, p. 357, fig. 5, p. 355. (Described and discussed. Fig. 5 

 is copied from fig. 5 of the preceding reference.) 



Oholella gemma Billings, Walcott, 1886, Bull. U. S. Geol. Survey No. 30, pp. 116-117, PI. X, figs. 2, 2a-e. (Copies 

 the original description, Billings, 1872a, pp. 218-219, and discusses species. The specimens represented by 

 PI. X, figs. 2b, 2c, 2d, and 2e, are redrawn in this monograph, PI. L, figs, li, Ij, Ik, and Ic, respectively.) 



Oholella gemma Billings, Walcott, 1891, Tenth Ann. Kept. U. S. Geol. Survey, p. 612, PL LXXI, figs. 5, 5a-c, PI. 

 LXXII, figs. 2 and 2a. (No text reference. Figs. 5, 5a-c are copied from Walcott, 1886b, PI. X, figs. 2, 2d, 2b, 

 and 2c, respectively; PI. LXXII, figs. 2 and 2a, are copied from Walcott, 1886b, PI. X, figs. 2a and 2e, respec- 

 tively.) 



Oholella gemma Billings, Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, pp. 69 and 71; 

 fig. 30, p. 71; and PL II, figs. 42-44. (Discussed under the genus Oholella. Fig. 30, p. 71, is copied from Wal- 

 cott, 1886b,Tl. X, fig. 2d; PL II, fig. 42, is drawn from the specimen figured by Walcott, 1886b, PL X, fig. 2a.) 



Bicia gemma (Billings), Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, pp. 678-680. (Described and discussed as 

 below.) 



General form ovate, with ventral valve subacuminate when the beak is extended, or 

 obtusely acuminate when the beak is rounded; dorsal valve oval to subcircular in outline; 

 the range of variation in the outline of the valves is shown by the jfigures on Plate L. The 

 convexity of the valves is fairly strong and nearly the same in each where they are embedded 

 in the same matrix. 



Surface of shell marked by numerous slightly irregular concentric striae and lines of growth, 

 by fine radiating strise between stronger radiating lines, and on some shells by strongly developed, 

 elevated, radiating strise; the radiating strise are often slightly irregular and interrupted, as 

 shown by figure la. When the outer surface is partly worn away it is smooth, or the shell 

 has a pecuUar surface formed by traces of the radiating, interrupted, or undulating strife (fig. 

 Id). The concentric strise and lines of growth are shown on the outer surface of the inner 

 layers of the shell and on the interior surface where rather strong radiating strife are often 

 beautifully shown. 



The shell is unusually tMck and strong for one so small; those from St. Simon and Troy 

 appear to be calcareous and formed of one solid layer; this is probably owing to their condi- 

 tion of preservation, as in a weathered specimen lamellae oblique to the outer surface are clearly 

 shown, and indications of lamellse on the central and posterior portions point to the same 

 shell structure as in Oholus and Oholella. 



