18 BRITISH PERMIAN BRACHIOPODA. 



(PI. II, fig. 45), from four to six ribs were only developed, and in this condition resem- 

 ble the var. Jonesiana of King ; but most examples of jSp. cristata possess from eight 

 to ten ribs ; while a remarkable and unusually large individual, obtained at Tunstall hill 

 by Mr. Kirk by (PL II, fig. 43 1 ), presented fourteen on either valve, and so closely did this 

 specimen resemble some of Sowerby's typical examples of the Carboniferous S. octoplicata, 

 that it is very probable if not entirely certain that Sp. cristata is at most but a variety 

 or race, slightly modified by time and circumstance, of the Carboniferous species. 3 In the 

 Permian period it was, however, in general a smaller shell, the number of ribs likewise 

 frequently less numerous (PL I, fig. 38 ; and PL II, fig. 44). The external surface and 

 ribs are intersected at close intervals by many concentric laminae, or ridges of growth. 

 Its shell-structure has been described by Professor King as closely perforated, the canals 

 being large, and (according to Professor M'Coy) half their diameter apart. 3 In the 

 interior of the ventral valve two short diverging dental or rostral shelly plates form the 

 fissure-walls, and between these a sharp elevated mesial septum arises, and extends along 

 the bottom of the valve from the extremity of the beak to less than half its length, the 

 sharp elevated extremity dividing the upper portions of the two spiral coils. In the dorsal 

 valve the spiral cones are attached to prolongations of the inner socket-walls, and occupy 

 a large portion of the interior of the shell with their numerous convolutions, 4 as may be 

 seen in the enlarged illustration (PL I, fig. 40), taken from a beautifully perfect individual 

 from Humbleton hill, and forming part of Mr. Kirkby's valuable collection. A short and 

 small mesial septum seems likewise to exist in the smaller valve. The dimensions taken 

 from two British examples have produced — 



Length 5, width 9^, depth 5 lines (the largest known). 

 4, „ 7, „ 4 lines. 



Loc. Sp. cristata does not appear to have been a very common fossil in England, 

 and especially so with its shell preserved. Professors Quenstedt and King, Mr. Howse, and 

 others have found it in the shell limestone of Humbleton and Tunstall hills, Hylton, 

 North Farm, and Tynemouth Cliff. On the Continent it is mentioned by Schlotheim, 

 Dr. Geinitz, and Baron Schauroth, from Glucksbrunn, Konitz, Possneck, Altenstein, 

 Schwaara, and Ropsen j and was found by Mr. E. Robert at Bell Sound, Spitzberg. 5 



1 This specimen was first figured by Mr. Howse, in pi. iv, figs. 5 and C, of the nineteenth volume of 

 the 'Annals and Mag. of Nat. Hist.,' January, 1857. 



2 See Spiriferina cristata, var. octoplicata, in our Part V., p„ 38. 



3 Professor King has described singular casts of the tubular perforations visible on the surface of the 

 greater number of internal casts from Humbleton hill. 



4 This and other individuals which I have been able to examine, have presented from eleven to twelve 

 convolutions in each of the spiral cones. The crural processes were not united by a shelly band, as was 

 found to be the case in some examples of Spiriferina rostrata. 



5 Refer to De Koninck's 'Nouvelle notice sur les fossiles du Spitzberg,' vol. xvi of the Academie Royale 

 de Belgique, No. 12 des Bulletins. 



