NO. 5 RHYNCHONELLOID BRACHIOPODS — COOPER 53 



Discussion. — The exterior characters of this genus, except for the 

 anterior costation, are most like Hemithyris. The general form of 

 the shell, the obscure, fine costellation of the umbonal region, and 

 the large foramen are suggestive of the northern genus. The deltidial 

 plates are conjunct, however, and there the resemblance ends. 



The specimens available for study of the interior are not good 

 because the muscle marks are obscure and the cardinalia partially 

 broken. Nevertheless some important details can be distinguished. 

 Inside the pedicle valve the pedicle collar is fairly long and slightly 

 elevated above the valve floor. The dental plates are solid but of the 

 receding type. They are separated from the valve walls by moderately 

 deep and wide umbonal cavities. The muscle field is large and reaches 

 to about midvalve, possibly somewhat beyond in old specimens. 



Inside the brachial valve the cardinalia are stout and thick. The 

 cardinal process is a thick, bilobed boss at the apex. The socket 

 ridges are thick and the crura are long, slender, and flattened hori- 

 zontally. These features are well shown in specimen U.S.N.M. 

 549423a. The crural bases are attached directly to the socket ridges 

 without outer socket plates. An inner thickening along the edge of 

 the crural bases suggests some development of inner hinge plates. 

 Median ridge small and inconspicuous. The cardinalia appear to be 

 related to those of Hemithyris, Notosaria, and Tegnlorhynchia. 



According to Jaanusson (1951, p. 196) the shell referred by Buck- 

 man (1910, p. 12) to Hemithyris plicigera should be referred to 

 Plicirhynchia. Jaanusson also points out in connection with Hemithy- 

 ris dibbleei and H. reagani, both of Hertlein and Grant (1944), that 

 these do not belong to Hemithyris but, because of their anterior 

 costation, may be assigned to Plicirhynchia. Unfortunately the in- 

 terior details of these two species are unknown and the suggested 

 assignment can only be tentative (see discussion of Hemithyris). 



FRIELEIIDAE Cooper, new family 



Genus FRIELEIA Dall, 1895 



Plates 4, B, 14, B, 15, A, 21, A 



Frieleia Dall, Proc. U. S. Nat. Mus., vol. 17, p. 713, 1895 ; Thomson, Geol. Mag., 

 n. s., dec. 6, vol. 2, pp. 389, 392, 1915; Jackson, British Antarctic ("Terra 

 Nova") Exped., 1910, Nat. Hist. Rep., Zool., vol. 2, No. 8, pp. 192, 193, 1918; 

 Thomson, New Zealand Board Sci. Art, Manual 7, p. 157, 1927; Hatai, Sci. 

 Rep. Tohoku Imp. Univ., ser. 2 (Geology), vol. 20, p. 219, 1940; Hertlein 

 and Grant, Publ. Univ. California at Los Angeles, Math, and Phys. Sci., vol. 

 3, P. 57, I944- 



