BRACmOPODA. 315 



the length of the valve. Muscular impressions small, quadruple, not dendritic, 

 the interior pair being sharply raised. The brachial ridges originate from 

 between the adductor scars, curving gently outward, recurving, at first grad- 

 ually and then abruptly to their anterior limit ; then turning suddenly back- 

 ward, and again inward horizontally, meeting the median septum near its 

 anterior extremity. 



Surface of the pedicle-valve covered with spines, which near the beak are 

 often curved backward, embracing some external object. In some species all 

 the spines of the valve have evidently been at least of accessory importance in 

 eftecting its attachment. The surface of the brachial valve may be either 

 spinous, lamellose or smooth. 



Type, Orthis excavata, Geinitz, = S. Goldfussi, (Miinster) Davidson. Permian 

 of Europe. 



Observations. The existence of cardinal areas, delthyria, and articulation, 

 the form of the brachial ridges, and the substantial attachment of the shell 

 either in youth or throughout its existence, make an association of characters 

 which serve to readily distinguish this genus from its allies. The genus 

 Strophalosia is not very abundant!}' represented in species ; all the generic 

 characters described are typically developed only in the Permian mem- 

 bers of the group.* In the earlier forms of the Devonian and Lower Car- 

 boniferous, the expression of the shells is often quite distinct from the later 

 species, though not affording any satisfactory basis for separation. The 

 existence of an articular system and of cardinal areas is not sufficient of itseli' 

 to distinguish Strophalosia from Productella; and it will therefore be neces- 

 sary to base distinctive generic value upon the umbonal attachment of the 

 former. 



In the mature condition of the Permian species the umbonal cicatrix of the 

 pedicle-valve is often obscure, having become somewhat obliterated, during 

 their probably free condition near, and at maturity. As observed in the 

 diagnosis, the spines in such species are frequently turned backward in such a 

 manner as to leave the impression that they were certainly flexible, and prob- 



* See Waaobn, Salt-Range Fossils ; Brachiopoda, p. 640. 



