42 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 39 



type, long and slender and with only a slight development of outer 

 hinge plates. The crura however are flattened horizontally as one 

 observes them from the posteroventral side and the distal extremi- 

 ties are quite thin. In Aphelesia the crura are long, broad, of falcifer 

 type, and the bases attached to the socket ridges with no development 

 of outer hinge plates. The distal ends of the crura, unlike Hemi- 

 thyris are scimitarlike, are laterally compressed and their distal ex- 

 tremities serrate. In cross section these crura are crescentic and the 

 convex surface faces laterally. The crural blades are broad and thick 

 and thus quite unlike those of Hemithyris. 



The crura of Aphelesia are like those of Rhytirhynchia, Neorhyn- 

 chia, and Basiliola but differ from all of them in the absence of outer 

 hinge plates which are so prominent in the other genera. Aphelesia 

 differs from these genera also in other important respects. 



Geological horizon. — Eocene through Pliocene. 



Geographic distribution. — Mediterranean region. 



Assigned species. — At present it is difficult to assign the several 

 species of Mediterranean Tertiary rhynchonelloids to their proper 

 genus because the interiors are poorly known or completely unknown. 



Anomia bipartita Brocchi, Pliocene, Italy. 



Terebratula plico-dentata Costa, Miocene-Pliocene, Italy. 



Rhynchonclla {Hemithyris) saccoi Patane, Pleistocene, Sicily. 



Hemithyris acuta Meznerics, Miocene, Hungary. 



Rhynchonclla bipartita psendobipartita Patane, Pleistocene, Sicily. 



Discussion. — These species have been assigned to Hemithyris at 

 one time or another but the exterior characters preclude such a place- 

 ment. The little that is known of the interior also excludes these shells 

 from assignment to Hemithyris. The beak characters and cardinalia 

 of Aphelesia as shown by A. bipartita are quite unlike the same fea- 

 tures of Hemithyris. The exterior of most of these shells is smooth 

 or nearly so. Some exhibit anterior costation but it is generally not 

 regularly developed. None of them have the fine striate exterior of 

 Hemithyris. The latter, too, has disjunct deltidial plates and an 

 elongate beak, whereas the beaks of the Italian species are short and 

 the deltidial plates conjunct. The crura of Hemithyris are long, 

 curved, and slender, quite different from the broad-bladed Aphelesia 

 bipartita. 



Aethehnae Cooper, new subfamily 



Genus AETHEIA Thomson, 19 15 



Plates 4, A, 9, B 



Aetheia Thomson, Geol. Mag., n. s., dec. 6, vol. 2, p. 389, 1915; Thomson, New 

 Zealand Board Sci. Art, Manual 7, p. 156, 1927. 



