52 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



T. coclata (Tension- Woods), Oligocene to Miocene, Tasmania and 



Australia. 

 T. masoni Allan, Miocene, New Zealand. 



Discussion. — As here limited, the name Tegulorhynchia is applied 

 only to imbricate species with cardinalia and hinge characters like 

 those of T. squamosa. 



Genus PLICIRHYNCHIA Allan, 1947 

 Plate 7, A 

 Plicirhynchia Allan, Journ. Paleont., vol. 21, No. 5, p. 493, 1947. 



Subtriangular to subpentagonal in outline with the maximum width 

 near the middle; inequivalve, the brachial valve having the greater 

 depth; anterior commissure uniplicate, the fold of the brachial valve 

 being conspicuous and fairly long ; surface ornate, the posterior half 

 being marked by fine radial lines and striae, the anterior half strongly 

 costate. Beak of the pedicle valve long, narrowly pointed, and nearly 

 straight ; foramen complete, large, longitudinally oval, hypothyrid ; 

 deltidial plates thick and conjunct. 



Pedicle valve interior with thick corrugated teeth supported by long, 

 stout dental plates ; pedicle collar long ; muscle field large and 

 flabellate, enclosing the adductor scars. 



Brachial valve interior with corrugated sockets bounded by thick 

 overhanging socket ridges ; crural bases attached directly to the 

 socket ridges; crura of radulifer type, long, horizontally flattened; 

 inner hinge plates strongly developed. Cardinal process thick and 

 bilobed. Median ridge small. 



Type species (by original designation). — Rhynchonella plicigera 

 von Ihering, Rev. Mus. Paulista, vol. 2, p. 270, text fig. 7, 1897. 



Comparisons. — This genus is characterized by its peculiar exterior 

 ornament, the posterior and umbonal regions being finely costellate 

 but the anterior half strongly costate. The only other semicostate 

 genus marked like this is Probolarina, but from that genus it differs 

 in beak characters, cardinalia, and the presence of a cardinal process. 



Geological horizon. — Plicirhynchia occurs in the Eocene (Pata- 

 gonian) of Argentina. 



Assigned species. — Only one species is assigned here with assur- 

 ance : 



Rhynchonella plicigera von Ihering. 

 ? Hemithyris plicigera Buckman, not von Ihering. 



Distribution. — Known only from Argentina and possibly from the 

 Antarctic. 



