30 BRITISH PERMIAN BRACHIOPODA. 



The sub-genus Streptorhynchus, as typified by Terebratulites pelargonatus of Schlotheim 

 (PL II, figs. 32 — 42), or by Leptana devonica, D'Orb., 1 may be characterised as 

 an inequivalved shell, convex or concavo-convex, externally striated. The smaller 

 valve is semicircular, the larger or ventral one possessing a prolonged and oftentimes 

 bent or twisted beak ; hinge-line rather shorter than the width of the shell. The area 

 in the larger valve is triangular, with a fissure covered by a convex pseudo-deltidium. 

 A small, narrow rudimentary area exists, likewise, in the smaller valve. No foramen is 

 observable, but the cardinal process is at times seen partially extending under the 

 deltidium, as in the woodcut (fig. 1, p. 29). 



In the interior of the larger or ventral valve (PI. II, figs. 40, 41 ; and woodcut, fig. 2) 

 a strong hinge-tooth is situated on either side at the base of the fissure, supported by a 

 dental ridge or plate ; these diminish in size as they converge under the area towards the 

 extremity of the beak (fig. 40 ; woodcut, fig. 2 t). At the bottom of the valve, under the 

 beak, and extending a little beyond, are the impressions left by the cardinal and adductor 

 muscles, which occupy about one third of the length of the valve ; they form two 

 elongated oval scars, more or less deeply excavated, and separated by a rather wide mesial 

 ridge (fig. 40 ; and woodcut, fig. 2 it). 



In the interior of the smaller or dorsal valve the cardinal process is largely developed 

 (figs. 38, 39 ; and woodcut, 3), being composed of two testaceous projections, which are 

 either slightly convex or concave on the side facing the interior, but grooved or bidentated 

 towards the extremity of their outer surface (fig. 39) ; the socket-plates are large, and 

 partly united to the lower portion of the cardinal process. Under these, on the bottom of 

 the valve, are seen the quadruple impressions left by the adductor, which occupy more 

 than a third of the length of the valve, and are arranged in pairs, divided by a short 

 rounded mesial ridge. 



1 Leptcena Devonica, D'Orbigny, 'Prodrome,' vol. i, p. 90, 1849 = Orthis crenistria, var. Devo- 

 nica, De Keyserling, from the Devonian beds of Ferques, which has long been confounded with Orthis 

 umbraculum, V. Buch, from the Eifel, certainly belongs to the same section as that typified by Strepto- 

 rhynchus pelargonatus. The woodcuts, figs. 2 and 3, have been made from interiors obtained at Ferques by 

 Mr. Bouchard and myself, and are essentially similar in internal character to those of S. pelargonata 

 (PI. II, figs. 38—41). 



The following differences have been pointed out by Mr. Bouchard as occurring between O. umbraculum, 

 V. Buch, from the Eifel, and O. Devonica, from the Devonian beds of Ferques : 



"The first is very constant in its shape, and in that of its area ; is concavo-convex — that is to say, its 

 smaller valve is convex, while the larger or ventral one is concave in all fully developed or adult individuals ; 

 on both valves the striae are strongly marked and granulated ; the area always regular and narrow. 



" Streptorhynchus Devonicus, D'Orb., is, on the contrary, very inconstant in its external form : one 

 does not meet with two similarly shaped individuals. It is always bi-convex — that is to say, both its valves 

 are convex, their striae smooth and not strongly marked. The area assumes every kind of shape, both iu 

 height and width ; is very often irregularly twisted, being wider than long on one side than on the other ; 

 the beak being curved backwards, or inclined to one or to the other side, nothing appearing regular in the 

 shell. Interiorly the details of both are similar." 



