Recent and Tertiary Rhynchonellids. 391 



with discrete deltidial plates, and is completely enclosed in a funnel- 

 shaped pseudo-deltidium in those species where the upper deltidial 

 plates unite, including Basiola beecheri (Dall). Basiola is merely 

 a Hemithyris in which the dorsal deltidial plates are united, a difference 

 hardly entitling it to separate generic rank. 



Hinge-teeth and Dental Plates. 

 The majority of Rhynchonellids have hinge-teeth in the ventral 

 valve supported by dental plates. This is the case in all the Tertiary 

 and Recent genera here noticed with the exception of JEtheia. 

 In Hemithyris the dental plates are slender but quite distinct, and 

 are clearly mentioned in the descriptions of species by Davidson, Dall, 

 and others. Nevertheless the statement is made by Hall & Clarke l 

 that dental plates are absent in this genus, and this error has been 

 copied by Schuchert, 2 and has led Buckman 3 to state that Hemithyris 

 imbricata is correctly placed under Hemithyris on account of the 

 apparent absence of dental plates amongst other characters. 4 



Cardinalia and Septa of Dorsal Yalve. 

 Cardinalia is a new term to embrace collectively the socket walls or 

 ridges, crural bases, hinge-plate, and cardinal process of the dorsal 

 valve. These parts are in some genera so intimately united that they 

 cannot be separately described, e.g. in Bouchardia. "When a septum 

 is present in the dorsal valve it often unites posteriorly with the 

 cardinalia. The socket-ridges are the processes forming the inner 

 walls of the dental sockets and bearing on their inner sides the crural 

 bases, hinge-plate, etc. They are by some authors confused with the 

 cardinal process, while Dall consistently speaks of them as the hinge- 

 teeth of the dorsal valve but as they do not fit into corresponding 

 sockets in the ventral valve, the other term of King is preferable. 5 

 A cardinal process, either resting directly on the apex of the valve, 

 or resting on an excavate hinge-plate supported by a septum, or resting 

 directly on the septum itself, is present in probably all the genera 

 of Recent and Tertiary Rhynchonellids. Schuchert 6 uses the supposed 

 absence of a cardinal process to separate some Palaeozoic and the bulk 

 of Mesozoic and later genera under the Rhynchonellinae from the early 

 Palaeozoic Rhynchotreminse, in which such a process is present. There 

 is certainly some misunderstanding here. 



1 "An Introduction to the Study of the Brachiopoda, etc." : 47th Ann. Rep. 

 New York State Museum, 1894. 



2 Loc. cit. 3 " Antarctic Fossil Brachiopoda," etc., p. 11. 



4 It is probable that Buckman's species has slender dental plates, for it 

 appears to be synonymous with H. squamosa (Hutton), in which they are 

 certainly present. Hutton gave no figure of the latter species, and his 

 description is meagre. An examination of the" holotype shows that the species 

 was misunderstood by Tate, who figured a much broader form under that 

 name, and in this Buckman followed him. H. cozlata (McCoy) is a more 

 coarsely ribbed species, while H. pyxidata, Davidson, has discrete deltidial 

 plates. 



5 W. King, A Monograph of the Permian Fossils of England, 1850, p. 68, 

 pi. xx, fig. 11. Schuchert speaks of these socket walls as hinge-plates, but this 

 is opposed to the usual convention (cf. H. Woods, Palceontology Invertebrate, 

 p. 158, fig. 65, b, 1902). 



6 Loc. cit. 



