-280 - 



ellae, near the ventral mar.p-in are orowfled and occasionally? in- 

 terrupted r '-olov/ the sharp edge of the lamella a lov; roxiy.ded un- 

 diilation usually developed; hinge normal. 



Dimensions ,- length, 4.8 mm.; alt., 4.5 mm.; semidiam., 

 1 mm. 



l^emarlrs . - '^n right valves the greater length and excava- 

 tion of the v- ior dorsal raarrin is deoir^ed; some left valves 

 are almost equilateral, but on the majority of them also the T)0st- 

 erior dorssl mar,frin is longer and more angular at its distal end. 

 The e^fre of the concentric laraell-e on the ventral half of the 

 shell is usually more or less croder\ so that the lamellae have 

 an irregular outline and may even he diseontinuo-. . "ear -^he vent- 

 ral m.ar~in "ortuitous sma" ler lamellae are not Infreouently inter- 

 calated hetvreen the larger ones. A slin-ht 'iepression is someti^f.es 

 present in front of the posterior "liarrin, rarely causing the vent- 

 ral marrln to he feehly insim^ateri. The Isr-e t valve has the fol- 

 lowing dimensions: length, 6 mm.; alt., 5.6 :: . ; semidiam.., l.S mm. 



The recent West Indian 0_. gi^adalupens 11: d ' Gr"bi?"ny (1; is very 



(1). In de la Sagra, ^-Tist. phvs., polit. et natur. de I'Isle de 

 Ouha, ITollusques, vol. 2, ^. ?-t, ^1. ?7, figs. 24-S6, 1855 

 ( ITrench ed, ) . 



close, hsving the same outline and the same type of sciilpture; 

 the only differences seem to lie in the tendency for the recent 



