346 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvi. 



Subgenus ^ora Conrad, 1870. Type, ^£. cretacea Conrad. Cre- 

 taceous. 



This is still imperfectly known, but differs from Dosiniojpsix chiefly 

 bv beino- smaller, more delicate, and of a more elongated form. 



Subgenus Pelecyora Dall, VM)'!. Type, Cytherea hatcJietigherii.sJx 

 Aldrich, 188(3. Eocene. 



Shell orbicular, with rugose nymphs, simple anterior lateral and 

 socket; no posterior lateral; the pallial sinus narrow, angular, ascend- 

 ing; the cardinals entire except the right posterior one, which is bifid; 

 otherwise as in .Dosmloj)si.s, though the only known species is very 

 much smaller than the known species of DoxiniojM!!'^. 



This group differs from Dosiniopsis by its smooth lateral and socket, 

 and by the absence of the posterior lateral and socket, and by its rela- 

 tively deeper pallial sinus. From ^E'>m the same characters, as well 

 as the nonbifid left cardinals and orbicular form, suffice to distinguish 

 it. The rugosity of the nymphs is more like the semiradial rugffi in 

 Tivela than the fine granulations of the type of Doslniojysis. 



B. Anterior lateral tooth and a delined liniide 2>r<'><eid. 

 Genus DOSINIA Scopoli, 1777. 



Type D. afrlmna Hanley (Le Dosin, Adanson, 1757). 



This is Cytherea (sp.) Bolten, 1798; OrUculus a and /i, Megerle, 

 1811; Art/ienu's (Poll) Oken, 1815; Asa (Leach) Basterot, 1825; Arcfoe 

 Kisso, 1826; Exoleta Brown, 1827; Artemis Conrad, 1832; Arctoa 

 Herrmannsen, 18-1:6; Gerana Gistel, 1848; Assa (Leach) Gray, 1851; 

 Ariiphlthcea Leach, 1852; but not Dosina Gray, 1838. 



Section Dosinia s. s. 



Lunule impressed, small; escutcheon narrow, elongate, flattish, bor- 

 dered on each side by a ridge or keel, at which the concentric sculpture 

 tends to become lamellose; middle cardinals often grooved or bifid, the 

 other teeth smooth; pallial sinus angular, ascending, usually narrow 

 and extended forward at least halfway from the posterior to the 

 anterior adductor; valves moderateh' convex. 



The form of the escutcheon differs in this group from an obscure 

 flattening, often unequal in the two valves, to a distinctly keeled area 

 with sculpture differing from that outside the boundary, but in the 

 series of species almost ever^^ gradation between these forms may be 

 observed. 



Section Orhlculns Megerle, 1811. Type, Yenus exoleta Linmvus. 



In this section there is no escutcheon, the pallial sinus is very long 

 and narrow, and the anterior lateral is strong. 



Orhlcidns i^ Megerle, founded on Venus jjrostrata Linnaeus, is a 

 typical Dosin la. Most of the generic s3mon3mis cited under the genus 

 were based on the conunon European species which is the type of this 



