32 BRITISH PERMIAN BRACHIOPODA. 



lateral depressions, which served no doubt as points of attachment to the cardinal muscles, 

 and is, moreover, entirely covered by the deltidium, leaving a deep conical hole on either 

 side. At a short distance under this is seen a large, strong, mesial ridge, 1 with two 

 lateral ones ; between these are situated, on the bottom of the valve, the quadruple im- 

 pressions left by the adductor (a) ; two deep holes (m), similar to those situated on either 

 side of the cardinal process, are likewise visible on either side, of the commencement of 

 the mesial ridge last described. 



These dispositions are also very different from those of Streptorhynchas, where the 

 cardinal process is bilobed and completely exposed ; nor are the other internal impressions 

 similar in their details. Professor King was therefore justified in his views, although he 

 was unacquainted at the time with several of the distinguishing internal characters of 

 D'Orbigny's genus. Much more, however, remains to be discovered before the numerous 

 species composing the family Strophomenid^e can be correctly classed, and we cannot be 

 too cautious in our inferences, as the example just given will sufficiently demonstrate. 



Streptorhynchus pelargonatus, Schlotheim, sp. Plate II, figs. 32 — 42 ; and King's 



Mon., pi. x, figs. IS— 28. 



Terebratulites pelargonatus, Schlotheim. Akad. Munch., vol. vi, p. 28, pi. viii, 



figs. 21—24, 1816. 



This little species, which in external shape bears much resemblauce to several species 

 of Thecidium, is more or less sub-conical or triangular. The smaller or dorsal valve is 

 semicircular, and slightly indented in front, with a shallow mesial depression or furrow, 

 commencing at a short distance from the extremity of the umbone ; it possesses, likewise, 

 a narrow rudimentary area. The hinge-line is shorter than the greatest width of the 

 shell. The ventral valve is convex, semi-conical ; the beak, in general largely developed, 

 and at times exceeding the length of the smaller valve, is produced, elevated, bent back- 

 wards, and often irregularly twisted either to the one or other side. The area is 

 large, triangular, with a fissure covered by a convex pseudo-deltidium. Externally the 

 valves are ornamented by numerous small radiating raised strise, which augment in number 

 at variable distances from the beaks, both by intercalation and bifurcation, and are like- 

 wise intersected by numerous concentric lines of growth. The internal details have been 

 alluded to under the generic characters. 



The dimensions attained by this little shell vary considerably in different countries and 



1 Septa are rarely developed in the smaller valve of Strophomenidce ; but in one species from the 

 Devonian beds of Ferques, Or this Beshaysii, Bouchard, there exists a largely produced mesial plate, which, 

 commencing under the cardinal process, extends almost to the frontal margin. 



