128 PERMIAN POSSILS. 



Spikifek ckistatus, Schl. Geinitz, Gsea von Sachsen, p. 97, 1843. 



— — „ Morris, Catalogue, p. 128, 1843. 



— — „ De Verneuil, Bull. Soc. Geol. de France, 2""' serie, t. i, 



p. 28, 1844. 



— — „ Geol. Russ., vol. i, p. 221, 1845. 



— — „ Tennant, Brit. Fossils, p. 88, 1847. 



— — „ King, Catalogue, p. 8, 1848. 



— — „ Howse, Trans, T. N. F. C, vol. i, p. 254, 1848. 



— — „ Geinitz, Versteinerungen, p. 12, pi. v, fig. 10, 1848. 



(?) — — „ De Koninck, Bull. Soc. Geol. de France, 2"° serie, t. vi, 



Seance June 2, 1849. 



Diagnosis. — Semi-elliptical marginally : with generally eight prominent angular 

 ribs. Surface with prominent lines of growth. Punctures large, giving the valves a 

 coarsely granulated appearance. Large valve half as high as it is wide, slightly rounded : 

 umbone slightly incurving : area moderately high : fissure moderately large, and open : 

 median plate deep, and extending from the umbonal point to the centre of the valve. 

 Small valve slightly elevated, and somewhat flat: median rib twice the size of those 

 immediately adjoining. 



Trigonotreta cristata closely resembles one or more so-called species found in the 

 Carboniferous and other formations, particularly the T. octoplicata of J. Sowerby. 

 Having examined in Mr. J. de C. Sowerby's collection the originals (from Derbyshire) 

 of the figures in the ' Mineral Conchology,' the only difference I could perceive is, that 

 they are wider than any examples which have occurred to me of the present species.' 

 Specimens bearing the name of Spirifera insculpta, in the Gilbertsonian collection 

 of the British Museum, appear to be undistinguishable from Trigonotreta cristata. 

 The Jurassic fossil which Zeiten has identified with the T. octoplicata, is another 

 closely analogous species. 



Its large punctures give " this species a remarkable appearance, particularly in 

 casts, which are often crowded with short truncated spines standing erect on the 

 surfaces to which they adhere ; the same being casts of tubular punctures, which 

 passed uninterruptedly through the entire thickness of the valves from the inner to 

 the outer surface. The punctures, and their casts, are represented, highly magnified, 

 in figs. 13, 14, PI. VIII. 



Trigonotreta cristata was first recorded as a British species by Quenstedt, who 

 notices its occurring at Humbleton. I have found it at Tunstall Hill, Hylton North 

 Farm, and Tynemouth Cliff; but in none of these localities is it a common fossil, 

 especially in the last three. Schlotheim, its earliest discoverer, noticed it at Gliicksbrunn ; 

 and Geinitz gives the following additional German localities, Konitz, Possneck, Alten- 

 stein, Schwaara, and Ropsen. If De Koninck be correct in the identification, it may 

 be stated as also occurring in Spitzbergen. It does not appear to have been found in 

 Russia. 



^ Mr. J. de C. Sowerby's specimens have punctures like those of Trigonotreta cristata. 



