BRACHIOPODA. 
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 
effecting its attachment. The surface of the brachial valve may be either 
spinous, lamellose or smooth. 
Type, Orthis excavata, Geinitz, = S. Goldfussi, (Munster) 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 abundantly 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 itself 
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 Waagen, Salt-Range Fossils; Brachiopoda, p. 640. 
