N0.1229. CAMBBIAX BRACinOPODA—WALCOTT. (577 



of the ventral 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 striking features in both of the known species of this 

 genus is the oblong oval boss that is present in the ventral valve of 

 most adult shells. It is situated on each side of the forward projecting 

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

 outward when the shell is subacuminate or transvers(^l_v Avhen the shell 

 is broadly rounded. In the dorsal valve of Jj. gemma it is not so well 

 defined as in B. whlttcivesL The boss is bounded b}^ the margin of 

 the base of the area, the narrow elongate sulcus containing the mar- 

 ginal muscle scars and the base of the main vascular sinuses. In B. 

 v'Jiifeavesi it reached its greatest development in both valves, resem- 

 bling in position and surface characters the posterior adductor scars 

 of the Craniida?. Somewhat similar bosses occur in the ventral valve 

 of Oholella crassa and OhoJas ajMlI'tnis, but they are not developed to 

 the extent they are in Bicia. 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 incloses a heart- 

 shaped visceral area in the ventral valve, closely circumscribing the 

 muscle scars. Its general course in the dorsal valve is suggested hy 

 the position of the musncle scars. 



Five pairs of muscle scars have been observed. The rather large 

 central scars in the dorsal valve are placed close to the broad median 

 ridge, a little back of the center; the small anterior laterals are slightly 

 in advance of the centrals on the median ridge, close to the median 

 line; the transmedian scars are almost under the edge of the area and 

 near the outer margin; the outside and middle laterals are slightly in 

 advance and further 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. Traces of individual scars have been 

 seen, but they can not be separated so as to identify them. The trans- 

 median and anterior lateral scars are close to the outer margin of the 

 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. vJiiteaves't. 



Type. — OholeUa geinma Billings; second species, Blcla tchlteavesi 

 Walcott. 



Ohsei'vations.- — Bicia is a form that combines many of the character- 

 istics of Obolella and Obolus. It resembles Obolella 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 



