- S22 - 



the ventral marg'in and in the umbonal region. The concentric lines 

 override the rihs hut rarel;y and then are very faint. Two large 

 right valves, i nrc-er than "'■Iip f^ne measured, that apparently' be- 

 long to this species, have rihs v.hich are notably rounde '^ and even 

 flattened at the ventral margin. As usual, young shells are more 

 rounded than adults. The angular ribs are the distinguishing fea- 

 tiure of this species, v;hich numerically is not a conspicuous ele- 

 ment of the Pecten fauna. 



As Dall pointed out, abb's Santo Domingian auft-usticostatus 

 aprrees with .Sowerby's description of ozy~oniis « '^he fact that this 

 form 1 s not similar to eny of those under the name oxygronus in 

 the Henilier collection, as Dr. Dall learned from Kr. Reid, should 

 not have much weight since it is evident that labels and shells 

 in that collection are improperly asv^oeiated, a confusion which 

 in all probability occurred after the completion of So";erby's 

 work. -i^he type of aup-ust i co s t at us is larger than the Bowden spec- 

 imens, with the median and posterior ribs sharply angular, the 

 summits of the anterior si::- or seven slightly rounded, the poster- 

 ior submarrin bearing weak radial s. 



Occurrence .- UT^^^er Oligooene: Santo Domingo (Sowerby, 1850; 

 Gabb, 1873; Dall, 1898); Lower Miocene: Bowden beds, 



Bowden, Jamaica (Dall, 1898). 



