BRACHIOPODA. 223 



the inner surface of the valve (P. latiplicata, P. mulliplicata). This feature seems 

 to some extent subject to variation within specific limits; that is, being more 

 or less of an individual peculiarity. 



The brachial valve of P. latiplicata and P. mvltiplicata shows four distinct 

 ovate muscular scars about the anterior prolongation of the median septum, 

 and these are of quite the same character as those in the corresponding valve 

 of Anastrophia. Indeed, in all of these species the interior structure does not 

 materially differ from that of Anastrophia, though, being a thin-shelled group, 

 the muscular impressions are not as clearly developed. In exterior characters, 

 however, the differences are more significant. 



To the six American species wliich are above referred to Pakastropiiia, are 

 probably to be added the Rhynchonella Scotica, Davidson, from the Llandeilo of 

 Ayrshire,* and the Pentamerus {Alrypa) rotundaius, Sowerby, from the Wenlock 

 of Wenlock Edge.f 



It is probable that upon a shell of similar structure to Parastrophia, Gagel 

 has recently based his proposed genus Branconia, B. bnrussica, from the Lower 

 Silurian diluvial boulders in Ostpreussen (Die Brachiopoden der cambrischen 

 und silurischen Geschiebe im Diluvium der Provinzen Ost- and Westpreussen : 

 Beitriige zur Naturkunde Preussens herausgegeben von der Physikalisch- 

 Oekonomischen Gesellschaft zu Konigsberg, p. 62, pi. iv, fig. 12. 1890). From 

 the description and figures of the exterior of a single specimen it appears to 

 be a trihedral shell of rhynchonelloid aspect, but with a median septum in each 

 valve. What the inner relations of these septa were, or any other interior 

 characters of the shell, is not made known. It seems very doubtful if the 

 author is correct in regarding the more convex valve as the ventral, and the 

 shallow valve as the dorsal, but it will be impossible to pass judgment on the 

 value of the genus as now defined. So early a representative of this structure 

 should receive further elucidation. 



* Davidson, Silurian Brachiopoda, Suppl. p. 201, pi. xi, figs. 26 o-d. 

 t Silurian Brachiopoda, p. 150, pi. xv, figs. 9-12 



