NO. 2 BRACHIOPOD SUPERFAMILY STENOSCISMATACEA — GRANT 23 



camarophorium. The crura also help outline this chamber and prob- 

 ably helped support the body wall of the animal. As in living rhyn- 

 chonelloids, the lophophore probably extended anteriorly from the 

 anterior body wall, and its support probably was fleshy, with the crura 

 lending support only to its base (Hyman, 1959). 



LOPHOPHORE 



The form of the lophophore cannot be observed directly because it 

 was not supported by a calcareous brachidium. However, if the Steno- 

 scismatacea are correctly classified as Rhynchonelloidea, the lophophore 

 probably was spirolophous, as in Recent representatives of that group 

 (Hyman, 1959). 



Rudwick (1962), in his analysis of the forms of the lophophores of 

 Recent brachiopods, called attention to Hancock's (1859) observation 

 that the various shapes are efficient to organize the requisite length of 

 lophophore to accommodate the number of filaments needed to feed the 

 organism at any particular stage of growth. Rudwick explained that 

 they must be arranged so that the filter chamber (the mantle cavity) 

 is divided into effectively isolated inhalent and exhalent chambers, 

 each with its own aperture. The spirolophe develops from the trochol- 

 ophus stage through the schizolophe, each of the two earlier stages 

 providing sufficient filamentous surface to feed the growing animal. 



Possibly all adult Stenoscismatacea were spirolophous. However, 

 the evolutionary increase in size, primarily exhibited in the Stenoscis- 

 matidae and suggested less strongly in the Atriboniidae, might mean 

 that the small early species could have fed efficiently with a schizolo- 

 phus lophophore (Rudwick, 1962, p. 598, fig. 6). 



PALLIAL MARKINGS 



Description. — Pallial markings in adult shells of the Stenoscismata- 

 cea begin about one-third the distance from the beak to the anterior 

 margin. A deep transverse groove, probably a gonocoel, extends from 

 the anterior edge of the median septum of the pedicle valve to each side 

 of the valve. The groove is rather deep in Permian silicified shells in 

 which it has been observed, and its anterior edge is a low ridge. Poste- 

 rior to this pair of grooves there are no clearly distinguishable pallial 

 marks. 



Pallial marks begin anterior to the transverse gonocoels as a pair of 

 shallow vascula media, one on each side of the median line. Each 

 vasculum bifurcates a f^w millimeters anterior to its beginning, and 

 each pair from this dichotomy also branches about the same distance 

 forward. Similar branching takes place at nearly equal intervals anteri- 

 orly, with about three or four dichotomies behind the margins of the 



