568 CAMBRIAN BRACHIOPODA. 



SubfamUy BICIIN2B Waleott and Sclm&liert. 



Genus BICIA Waleott. « 



Bida Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, pp. 676-678. (Described and discussed as below as a new genus.) 

 Bida Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PI. XI, and pp. 142 and 144. (Classification of genus.) 



Shell subequivalve, moderately convex, longitudinally ovate, with the ventral valve 

 sometimes subacuminate and the dorsal valve subcircular. Beak of both valves as now 

 known terminates at the posterior margin. Surface marked by concentric and radiating 

 striae. 



Shell substance unknown in an unaltered condition. Shell structure formed of a thin 

 surface layer and numerous inner layers or lamellse more or less oblique to the outer layer. 

 Area of the ventral valve usually on the plane of the edges of the valve, but in some instances 

 it rises at a low angle; it is usually high and triangular in outline, but the apex may be rounded 

 and the base curved forward at the median line; divided midway by a narrow pedicle furrow 

 and again at each side by a narrow flexure line that extends forward and outward from the 

 apex. Area of dorsal valve short; it appears in both of the known species to rise from the 

 plane of the edges of the valve. Strise of growth subparallel to the base across the areas. 



The main vascular sinuses of the ventral valve are narrow and extend forward from the 

 projecting center of the base of the area, gradually separating as they cross the visceral area 

 and extend forward beyond the transverse center of the shell. In the dorsal valve they appear 

 to separate more rapidly and to follow the outer margin of the central cavity, except in the 

 second species. A narrow median septum is indicated in the dorsal valve on the crest of a 

 strong median ridge. 



One of the strildng features in both of the known species of this genus is the oblong oval 

 boss (b) that is present in the ventral valve of most adidt shells; it is situated each side of 

 the forward projecting central portion of the area, with the larger axis extending forward and 

 outward when the shell is subacuminate, and transverse when the shell is broadly rounded; 

 in the dorsal valve of Bida gemma (Billings) it is not so well defined as in B. wMteavesi Wal- 

 cott; the boss (b) is bounded by the margin of the base of the area, the narrow elongate sulcus 

 containing the marginal muscle scars and the base of the main vascular sinuses. In B. wMt- 

 eavesi it reaches its greatest development in both valves, resembling in position and surface 

 characters the posterior occlusor scars of PJwlidops implicata von Huene [1899b, p. 278, PI. X]. 

 Somewhat similar bosses occur in the ventral valve of OholeUa crassa (Hall) and Oholus apoUinis 

 Eichwald, but they are not developed to the extent they are in Bida. They appear to occur 

 only in those thick shells that have deposits of shell substance over the visceral area. 



The outline of the parietal scar in the ventral valve is well shown by Plate L, figure Ig; 

 it incloses a heart-shaped visceral area in the ventral valve closely circumscribing the nniscle 

 scars; its general course in the dorsal valve is suggested by the position of the muscle scars. 



Five pairs of muscle scars have been observed. The rather large central scars (h) in the 

 dorsal valve are placed close to the broad median ridge, a little back of the center; the small 

 anterior laterals (j) are slightly in advance of the centrals on the median ridge, close to the 

 median line; the transmedian scars (i) are almost under the edge of the area and near the 

 outer margin; the outside (1) and middle (k) laterals are slightly in advance and farther out 

 than the transmedian scars. The centrals, middle laterals, and outside laterals of the ventral 

 valve are grouped in the narrow space on each side of the U-shaped forward-projecting portion 

 of the visceral area (c, fig. 2) ; traces of individual scars have been seen, but they can not be 

 separated so as to identify them; the transmedian (i) and anterior lateral (j) scars are close 

 to the outer margin of the ventral valve and just in advance of the oblong boss in front and 

 each side of the forward-projecting base of the area; umbonal and pedicle scars unknown, 

 except what may possibly be a small umbonal scar in the dorsal valve of B. whiteavesi Walcott 

 [PI. L, fig. 2e, at g]. 



a Prior to the definition of the genus Bida the type species was described under the following genera; 



Obolella Billings [1872a, p. 218; 1872b, p. 357]. I Obolella Hall and Clarke [1892c, pp. 69 and 71]. 



Obolella Walcott [1886b, p. 116; 1891a, p. 612]. | 



