3S BRITISH CARBONIFEROUS BRACHIOPODA. 



Spiriferina cristata, var. octoplicata, J. de C. Sowerby. Plate VII, figs. 37 — 47. 



Spirifer octoplicatus, Sowerby. Min. Con., p. 120, pi. 562, tabs. 2, 3, 4, May, 



1827. 



— cristatus, V. Buck. Ueber Delthyris, p. 39, 1837. 



— — M'Coy. Synopsis of the Carb. Foss. of Ireland, p. 133 ; and 



British Palaeozoic Fossils, p. 418, 1855. 



Spec. Char. Transversely sub-rhomboidal, valves about equally convex, and at times 

 rather gibbous ; hinge-line as long as the greatest width of the shell. Cardinal angles 

 acute or slightly rounded j area concave, triangular, and of variable width, fissure partly 

 covered by a pseudo-deltidium ; beak small and incurved. The mesial fold of the dorsal 

 valve is more often composed of a single rib which is much larger than those situated on 

 the lateral portions of the shell ; its crest being in general rounded from the umbone to 

 about half its length, when it gradually becomes more and more flattened as it ap- 

 proaches the frontal margin (fig. 38), but at times it remains angular during its entire 

 length, with a tendency to the formation of a rudimentary plait on either of its slopes, so 

 that in these rarer cases the fold assumes towards the front an obscurely triplicated appear- 

 ance (fig. 37). The sinus in the ventral valve is deep, acute, and generally simple, but 

 also more rarely interrupted by a rudimentary rib, which becomes visible in the proximity 

 of the front. 



The valves are ornamented by from eight to twelve angular ribs, which are, as well as 

 the sinus and fold, intersected by closely disposed, concentric, scale-like lamina?. The 

 surface of the shell is also closely beset by numerous small granular (spinose) asperities ; 

 the shell-structure being likewise perforated by minute tubuli or perforations. 



In the interior of the ventral valve there exists a sharp elevated mesial septum, which 

 rises from the bottom of the valve, and partly divides the spiral cones. Dimensions very 

 variable. Three examples, of which the first two are Sowerby's original types, have 

 afforded the following measurements : 

 Length 9, width 13, depth 8 lines. 

 6, „ 11, „ 6 lines. 

 5, „ 8, „ 5 lines. 

 Obs. The shell under description seems to have been mistaken and misunderstood by 

 the various authors who have commented upon its characters and affinities. It is very 

 variable in shape, and but rarely possesses the definite number of ribs which its name 

 would imply. The area is also very variable in its dimensions as well as in the angle it 

 forms with the level of the smaller valve, as may be seen from a glance at figures 41 

 and 43. Its affinities with the Permian Sp. cristata of Schlotheim (' Akad. Munch.,' 

 vol. vi, p. 28, pi. i, fig. 3, 1816) did not escape the notice of Baron Von Buch in 1S37, 



