570 CAMBEIAN BRACHIOPODA. 



The ventral valves average about 5 mm. in length, the largest being 7 mm. ; average width 

 4 mm., largest 5 mm. The dorsal valve is about one-fifth shorter than the ventral. 



The area ' f the ventral valve is usually on the plane of the margins of the valve, but in 

 many specimens it rises at angles varying from 1° to 10°; it is high and narrow, somewhat 

 as in Obolus (Schmidtia) acuminatus Mickwitz (PI. XIV, figs. 2, 2a) and divided midway by 

 a strong, rounded, narrow pedicle furrow; the striae of growth are rather coarse and arch 

 forward at the center and across the pedicle furrow, following the contour of the base of the 

 area; the position of the flexure line is sometimes clearly shown by a narrow depression. The 

 area of the dorsal valve is short and easily escapes observation except in well-preserved sheUs; 

 it sometimes has a slight central pedicle depression and often is only a short, almost smooth 

 surface extending well out on the cardinal slopes of the valve. 



The muscle scars as far as determined are arranged as in Oiolus. The umbonal and pedicle 

 scars have not been observed. The elongate, oval central scars (h) are rather large in the dorsal 

 valve and situated on each side of the strong median ridge about the middle of the valve; in 

 the ventral valve they are crowded in with the scars of the middle and outside laterals; the 

 anterior laterals (j) are barely discernible in one specimen of the dorsal valve as small oval dots 

 on the central ridge a short distance in advance of the centrals; in the ventral valve they are 

 close to the base of the area and near the outer edge of the shell; the middle and outside 

 laterals in the ventral valve are situated in the trapezoidal area (c), but do not appear to be 

 separable on the specimens in the collection; in the dorsal valve they are well shown in 

 advance of the transmedian scar (i). The latter (i) in the ventral valve is merged with the 

 anterior laterals (j). 



Of the vascular markings the main sinuses of the ventral valve are about all that is clearly 

 shown, although the position of the parietal scar is indicated in advance of the center of the 

 sheU (fig. Ig). One of the most strongly marked characters of the dorsal valve is the median 

 ridge (mr); it varies in strength and outHne in different shells, but is usually a prominent 

 feature; it extends to the frontal margin in most shells, but in some it narrows and is less 

 prominent anteriorly. A few specimens show a sHght depression crossing it just in front of 

 the central scars, and one has two minute anterior lateral muscle scars directly on the ridge, 

 the parietal scar passing across just in front of them. The thickened shell beneath the visceral 

 cavity of the ventral valve is present in nearly all adult shells; it varies greatly in size, form, 

 and thickness; in some valves it covers the entire area within the parietal scar (PI. L, figs. 

 Ih and Ik), and in others only a portion (PL L, fig. li). The thickening in the dorsal valve 

 is along the posterior border of the central cavity; this is best shown in the cast (PI. L, fig. 1 1). 

 The median ridge is also frequently more or less enlarged. 



Formation and LOCALrrv. — Lower Cambrian: (2o) Limestone bowlders in conglomerate on shore at east entrance 

 to harbor at Bic, Rimouski County; (2p) limestone on south side of the road a little west of Bic, and half mile (0.8 

 km.) west of the road leading to the wharf, Rimouski County; and (319b) limestone bowlders in conglomerate at 

 St. Simon, Rimouski (?) County; all in the Province of Quebec, Canada. 



(3920 [Billings, lS72a, p. 218]) At the Straits of Belleisle, Labrador. 



(32a) Limestone 0.75 mile (1.2 km.) west of Riders Mills on the Harlem Extension Railroad, about 9 miles 

 (14.4 km.) north-northeast of Chatham, Kinderhook quadrangle (U. S. Geol. Survey), Columbia County; (27) even- 

 bedded and conglomeratic limestones on the ridge in the eastern suburb of Troy, Rensselaer County ; (29a) limestone 

 1 mile (1.6 km.) below the New York Central Raihoad depot at Schodack, Rensselaer County; and (2b) limestone 

 just north of Beman Park, in the northeastern part of the city of Troy, Troy quadrangle (U. S. Geol. Survey), 

 Rensselaer County; all in New York. 



BiCIA WHITEAVESI Walcott. 



Plate L, figures 2, 2a-e. 



Bida whiteavesi Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, p. 680. (Characterized and discussed as below as a 

 new species.) 



This species is associated with Bicia gemma (Billings) in a bedded limestone at Troy, 

 New York. It differs from the latter, in the dorsal valve, in the absence of the median 

 ridge ; the presence of a broad area ; in the presence in the interior of both valves of two large, 



