54 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



ium : sessile in posterior for about 1 mm., elevated on low median sep- 

 tum duplex for most of length ; spondylium extending anteriorly about 

 half length of valve. 



Brachial valve interior with flat, undivided hinge plate; camaro- 

 phorium separate from hinge plate, connected to it by intercamaro- 

 phorial plate, elevated on high median septum, extending anteriorly 

 slightly beyond spondylium ; septum extending along floor slightly less 

 than half length of valve. 



Table 5. — Measurements of Atribonium kernahani 



Measurements, in millimeters 



Comparisons. — Atribonium kernahani is characterized by its small 

 size, strongly wedge-shaped profile, high narrow fold, sharp and 

 slightly attenuate beak, and normally recurved anterior flanks on the 

 pedicle valve. Its profile is most like that of A. gainesi (Nettelroth) 

 and A. succiduum n. sp., but it differs in its smaller size, flatter ante- 

 rior surface, and its fewer costae. In addition, many specimens of A. 

 succiduum are less wedge-shaped, and less abruptly flattened at the 

 anterior. The small size and sharp wedge shape distinguish A. kerna- 



