SPIRIFERA. 13 



possess likewise an unusually large hinge-plate, as well as two singularly shaped ap- 

 pendages, which, arising from the inner socket walls, follow an inward direction. No 

 other member of the Spiriferidae have presented those arrangements ; and it is possible 

 that when the interior shall be completely known, that they may be considered of more 

 than sub-generic importance. As to Cyrtia, Retzia, and Uncites, much requires to be 

 done before their characters or value as sub-genera can be completely determined. 1 In 

 the British Permians, the genera Spirifera, Athyris, and the sub-genus Spiriferina, are 

 hitherto alone represented. 



Genus — Spirifera, Sowerby. 

 (See General Introduction, Vol. I, p. 79, 1853.) 



Spirifera alata, Scldotheim, sp. Plate I, figs. 23 — 36 ; PI. II, figs. 6, 7. (King's 



Monog., pi. ix, figs. 1 — 17.) 



Terebratulites alatus, Schlotheim. Leonhards. Taschenbuch, vol. vii, p. 58, pi. ii, 



figs. 1, 2, 3, 1813. 



— undulatus, J. de C. Sowerby. Mineral Conchology, vol. vi, p. 119, 



pi. 562, fig. 1, March, 1827. 



— Cordieri, Robert. Atlas du Voyage de la Commission scientifique 



du Nord, pi. xix, fig. k, 1845. 



S. alata varies considerably in shape, according to age and individual. When 

 adult or full grown it is transversely fusiform, being twice, and even three times, as wide 

 as long (PI. I, figs. 23 and 27). Valves convex, deepest at a short distance from the 

 umbone ; hinge-line as long as the greatest width of the shell, the cardinal extremities 

 being more or less attenuated in different individuals. The area is wide, with sub-parallel 

 sides ; fissure triangular, and in great measure covered by a convex pseudo-deltidium ; 

 a narrow rudimentary area may be seen likewise in the smaller valve ; beak small and 

 incurved. The mesial fold is simple, of variable width, and flattened along its upper 

 surface ; while in the ventral valve there exists a shallow sinus, interrupted by the presence 

 of a rounded, slightly elevated mesial rib. The valves are likewise ornamented by a 

 variable number of rounded, or but slightly angular, ribs ; these are simple, or here and 

 there augmented by an occasional intercalation. In number they vary from about eight 

 to thirty on each valve, the larger number occurring on the most adult individuals. The 



1 I have published these few observations in the second volume of the ' Bulletin de la Soc. Linneenne 

 de Normandie,' 1857. 



