610 GAMBEIAN BRACHIOPODA. 



The description of the species includes that of the genus, as there is only one species now 

 known. 



Type. — Oholella circe Billings. 



The generic name is derived from the city of Quebec, near which the type species occurs. 



y QuEBECiA CIRCE (Billiugs) . 



Plate CIV, figures 7, 7a-g. 



Oholella circe Billings, 1872, Canadian Natiiralist, 2d ser., vol. 6, No. 2, pp. 219-220. (Described and discussed as a 



new species.) 

 Oholella circe Billings, 1872, Am. Jour. Sci., 3d ser., vol. 3, pp. 357-358. (Copy of preceding reference.) 

 Oholella dree Billings, Walcott (in part), 1886, Bull. U. S. Geol. Survey No. 30, p. 118, PI. X, fig. 3a (not fig. 3). 

 (Original description, Billings, 1872a, pp. 219-220, copied. The specimen represented by fig, 3a is redrawn in 

 this monograph, PI. CIV, fig. 7e. Fig. 3 represents a specimen of Oholella chromatica.) 

 Oholella circe Billings, Walcott (in part), 1891, Tenth Ann. Rept. U. S. Geol. Survey, p. 611, PL LXXI, fig. 3a (not 

 fig. 3). (Mentioned. Fig. 3a is copied from Walcott, 1886b, PI. X, fig. 3a. Fig. 3 represents a specimen of 

 Oholella chromatica.) 

 Billingsella circe (Billings), Waicott, 1901, Proc. U. S. Nat. Mus., vol. 23, p. 673. (Merely changes generic reference.) 

 Quebeda circe (Billings), Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 320-321. (Described and discussed essen- 

 tially as below.) 



General form broad ovate, with front and sides uniformly rounded, planoconvex. Surface 

 marked by fine concentric strias of growth. A ventral valve 3.5 mm. in length has a width of 

 4.5 mm. A dorsal valve 4.5 mm. in length has the same width; a larger dorsal valve, 11 mm. 

 in length, has a width of 10.5 mm. Shell rather thick, and composed of calcite in its present 

 condition. 



The ventral valve has an elevated umbo terminating in a sharp upward-pointing apex 

 that may be perforate; from the umbo the surface, in young shells, slopes so rapidly that the 

 central and outer portions of the shell are nearly flat, but in older shells moderately convex; 

 area short and divided midway by a relatively broad delthyrium that is nearly covered by a 

 convex deltidium; the inner surface is marked by fine, elevated, rather widely separated, radi- 

 ating strise and very fine punctse ; the very broad main vascular sinuses arch forward from a 

 point beneath the umbo and inclose a small, sUghtly elevated visceral area; a strong cardinal 

 tubercle occurs on each side of the pseudo-area (cl, PL CIV, figs. 7a and 7b) which was probably 

 the point of attachment of the cardinal muscle, i. e., transmedian and anterior laterals. 



Dorsal valve gently convex in young shells, becoming strongly convex in old shells; no 

 traces of an area have been observed — if present it must have been short and very low, as the 

 beak is nearly at the plane of the margins of the shell ; casts of the interior show that the valve 

 was thickened beneath the umbo by a ridge that separated what may be called the umbonal 

 cavity from the main cavity of the valve. On the cast of an old shell a rounded, narrow, longi- 

 tudinal, median ridge divides the umbonal cavity; on each side of the cavity and beyond it 

 there is the strongly marked path of advance of the transmedian muscle scars; in front of the 

 transverse ridge two strong ridges that extend toward the center of the valve occupy the position 

 of the main vascular trunks ; in one specimen a narrow groove extends from the central muscle 

 scar along the inside margin of the ridge (PL CIV, fig. 7). 



The muscle scars now known are the transmedians and centrals ; the former are situated 

 close to the margin of the valve, and the space assigned them may also include the posterior 

 laterals; the central scars are well indicated in several specimens, but no trace has been found 

 of the anterolaterals. The cardinal tubercle (cl) includes the space that was occupied by 

 the several points of attachment of the posterior muscle, i. e., transmedian, outside lateral, 

 and middle laterals; the cast of the tubercle is an elongate depression just inside the margin 

 of the shell. 



Observations. — By incorrect interpretation, both Mr. Billings [1872a, p. 220] and myself 

 [1886b, p. 118] identified the dorsal valve of the species as the ventral, and I illustrated [1886b, 

 PL X, fig. 3] a dorsal valve of Oholella chromatica as the dorsal valve of "0. circe." When 



