BRITISH CARBONIFEROUS BRACHIOPODA. 277 



Productus Llangollensis, n. sp. ? Plate XLV, figs. 1 — 6; Plate LV, figs. 9 — 10. 



Sjo. Char. Shell large, almost circular or transversely semicircular, concavo-convex ; 

 hinge-lines straight, usually shorter than the width of the shell. Ventral valve enor- 

 mously thick and ponderous, very convex ; beak rounded and much developed ; area 

 narrow, rarely exceeding a line in width ; fissure triangular. Dorsal valve moderately 

 concave ; area very narrow ; surface of both valves finely striated, three of these occupying 

 the width of a line. 



The ventral valve in some examples has attained nearly one inch in thickness. In the 

 interior, on each side of the fissure, are two strong, projecting teeth, and under these 

 commences a large, pyriform, muscular cavity, which extends to beyond half the length of 

 the valve, and occupies about a third of its inner surface, the greatest breadth being 

 situated towards the centre of the shell. In this depression three distinct pair of mus- 

 cular impressions are visible, which are separated to a greater or lesser extent by three 

 longitudinal ridges, the first central pair, or those situated nearest to the extremity of the 

 beak, occupy the two sides of the central ridge, and which ridge is far more prominent or 

 elevated than the other two ; these impressions, which also extend sometimes a little 

 beyond the limits of the central ridge, are due to the adductor (a) ; and still lower down, 

 towards the centre of the valve, are two smaller, sharply defined, obliquely oval-shaped 

 scars (c) (c in Productus, PI. XXXVII, fig. 1), and which are supposed to be due to 

 another attachment of the same muscle (?) ; while outside of these there exists a large, 

 elongated impression, referable to the divaricator or cardinal muscle. It is somewhat 

 singular that the small accessory adductor impression (c) had not been hitherto observed, 

 either by M. de Koninck or by myself, but in the specimens recently found they are 

 unmistakably defined. 



If we now compare the interior of this valve with that of several species of Productus, 

 we shall find that, excepting the dental processes, the muscular impressions would agree in 

 all essential conditions with those of Productus. The relative position of the adductor and 

 divaricator impressions varies somewhat in different species of the genus, as we have 

 already described ; thus, in P. giganteus, P. longispinus, &c., the divaricators are situated 

 immediately under and outside of the adductor, while in P. pustulosus, P. humerosus, &c, 

 the adductor is located between the two divaricator impressions, as in the case of 

 P. comoides. 



In the interior of the dorsal valve, under the large V-shaped cardinal process, there 

 exists a longitudinal ridge, which extends to two thirds the length of the valve, being 

 widest, rounded, and grooved near its origin under the cardinal process, but becoming- 

 narrower and more elevated towards its extremity. On either side of the cardinal 

 process there exists depressions for the reception of the teeth of the opposite valve, while 



