Recent and Tertiary Rhynchonellids. 



389 



valve without septum, hinge-teeth supported by dental plates. 

 Muscular impressions obscure. 



Folding of the Cincta type is rare amongst Rhynchonellids, but 

 is exhibited by tbe Triassic Halorella, Bittner. Frieleia, Dall, is 

 practically non-plicate, but it seems from Dall's description that 

 there is a faint sinus in each valve. 



Characters of Beak and Delthyrittm. 

 Buckman 1 has introduced the terms ' hypothyrid ' and 'epithyrid' 

 to designate two contrasted types of beak characters, a shell being 

 hypothyrid when it exhibits a distinct oval or circular opening below 

 the apex, and epithyrid when it exhibits a truncate perforate beak. 

 The possession of hypothyrid beak characters is an almost constant 

 characteristic of Rhynchonellids, but TerebratuZoidea, Waagen, and 

 Peregrinella, Oehlert, are epithyrid with large foramens. There is 

 a Tertiary series of Rhynchonellids, mostly smooth, which exhibits 

 epithyrid beak characters with minute foramen, and these require 

 generic recognition. 



JStheia, gen. nov. 

 Genotype Waldheimia (?) sinuata, Hutton 2 = Terebratula gaulteri, 



Morris. 3 



Fig. 1. — JEtheia gaulteri (Morris), Oamaruian, New Zealand : a, holotype of 

 Waldheimia sinuata, Hutton, Curiosity Shop, Canterbury ; b, interior 

 of posterior part of dorsal valve, showing septum and cardinalia (crura 

 broken), Squire's, South Canterbury. 



Dorsally uniplicate. Beak epithyrid, with a minute foramen. 

 Dorsal valve with high socket ridges, and a short stout low septum, 

 rising rapidly posteriorly, fusing with the crural bases and supporting 

 a short cardinal process. Hinge-teeth of ventral valve transversely 

 striated, not supported by dental plates. Muscular impressions small 

 but well marked, posterior, close. The genotype is perfectly smooth. 



Buckman has described a smooth Rhynchonellid from the Antarctic 

 Miocene under the name of Hemithyris australis, and states that 

 it belongs to the Rhynchonella lipartita series, in which he apparently 

 places also it!, bolcen&is (Massalongo) and R. lucida, Gould. R. lipartita 



1 Ann. Mag. Nat. Hist., ser. vn, vol. xviii, pp. 322-3, 1906. 



2 Cat. Tert. Moll. Ech. New Zealand, 1873, p. 36. 



3 Quart. Journ. Geol. Soc, vol. vi, p. 329, pi. xxviii, figs. 2, 3, 1850. The 

 type of this species is lost, and some doubt may attach to the identification of 

 W. sinuata, Hutton, with it. As the internal characters of the genus have 

 been worked out on specimens agreeing with the type of the latter species, it is 

 chosen for the genotype. 



