NO. 2 BRACHIOPOD SUPERFAMILY STENOSCISMATACEA — GRANT II 



through the Permian. Genera that lack the stolidium are included in 

 the family Atriboniidae n. fam. that ranges from Early or Middle 

 Devonian through the Permian. 



Species of the genus Coledium n. gen. that occur in the Upper Mis- 

 sissippian (Chester) are near the morphologic division between the 

 two families. The stolidium is narrow and may be absent from some 

 individuals (i.e., it is not preserved on all specimens), but the shape of 

 the shell is similar to that of smooth specimens of Stenoscisma schlo- 

 theimi (von Buch) from the Permian of Germany. Devonian and 

 Early Mississippian species of Coledium normally lack the stolidium. 



Presence of a stolidium, while important within the Stenoscismata- 

 cea, is not a defining characteristic of that superfamily. Many genera 

 in other groups have similar structures that may well be homologous 

 or have served the same function. Several genera within the Triplesi- 

 acea have marginal frills ; examples are Streptis Davidson, Cliftonia 

 (Cliftonia) Foerste, C. (Plectotreta) Ulrich and Cooper, and C. (Oxo- 

 plecia) Wilson, all of which are described and illustrated by Ulrich 

 and Cooper ( 1936) . Among the Athyridae, Athyris M'Coy and Actino- 

 conchus M'Coy have frills on many of the growth laminae, begin- 

 ning with some of the earliest. Apparently stolidia were not features 

 of maturity in these genera (for illustrations see Sarycheva (editor), 

 1960). The common genus Atrypa Dalman also has frills on juvenile 

 as well as adult parts of the shell (Fenton and Fenton, 1932 ; Cooper, 

 1944). 



Among groups more nearly related to the Stenoscismatacea, the 

 rhynchonelloid genus Sphaerirhynchia Cooper and Muir- Wood has a 

 rudimentary protuberance at the commissure, reminiscent of the in- 

 cipient stolidium of many species in the Atriboniidae and many speci- 

 mens of Coledium. Uncinulus velifer Gemmellaro (1899, pi. 26) has a 

 similar structure and, except for its typically rhynchonellacean dental 

 plates and median septum, it might be assigned to the Stenoscismatacea. 



The trail on many productaceans may be analogous to the stolidium 

 of the Stenoscismatacea, although in most genera it appears to have 

 formed in a different way. Instead of being a fundamental change in 

 direction of growth of both valves, normally the trail is a continuation 

 of the pedicle valve, with corresponding conformity of the edge of the 

 brachial valve. Institella Cooper and Limbella Stehli, however, have a 

 marked change in direction of growth of the pedicle valve to form a 

 relatively broad and flexuous marginal frill (Muir- Wood and Cooper, 

 1960), much as in the strophomenacean genera Leptaena Dalman and 

 Limbimurina Cooper (see Cooper, 1956b, p. 820, 851). 



Evolution. — Devonian species in the Stenoscismatacea lack the stoli- 

 dium, as do most species in the Mississippian. However, the margins 



