50 BRITISH PERMIAN BRACHIOPODA. 



two posterior muscular impressions were perfectly displayed, while the anterior or central 

 ones were much concealed by the matrix. The dimensions of the largest example were 

 — length 4, breadth 5^ lines. 



About fifteen examples of this interesting species were discovered by Mr. Kirkby in 

 the shell limestone of Tunstall hill. In external form it bears much resemblance to many 

 species of Cranium; but the peculiar spinulose character, combined with its sub-quadrate 

 shape, distinguishes it from those species to which it bears the nearest affinity. This is 

 also the first time that a Cranium has been recorded from the Permian rocks, a discovery 

 entirely due to the active researches of Mr. James Kirkby, to whom I take the greatest 

 pleasure in dedicating the species. 



Family— DISCWIDM 



{Vide General Introduction, Vol. I, p. 126.) 



Discini Koninckii, Geinitz. Plate IV, figs. 27 — 29. 



Orbicula Koninckii, Geinitz. Grundriss. d. Verst., p. 495 ; and Versteinerungen, 



pi. iv, figs. 25, 26, April, 1848. 

 Discina speluncakia, King. Mon., pi. vi, figs. 28, 29. 



Circular, or oval marginally ; the upper valve conical, and of moderate elevation ; the 

 vertex sub-marginal, situated at a variable distance from the posterior margin. The lower 

 valve is almost flat, with a fissure extending from the centre to nearly the edge of the 

 shell. The valves are strongly marked by numerous concentric lines of growth. In 

 dimensions it rarely exceeds 3 or 4 lines in length, by 3 or 3^ in width. 



Discina Koninckii appears to be one of the rarest of our British Permian fossils, 

 as I have never seen more than five or six examples. It has been collected at Thrislington 

 Gap, in the marl slate ; at Garmundsway, in the overlying beds of compact limestone ; in 

 the shell limestone of Tunstall hill, by Professor King ; and in the last-named locality, 

 and at Humbleton hill, by both Messrs. Howse and Kirkby. On the Continent it 

 appears also rare ; and I am indebted to Baron Schauroth for examples from Ilmenau, in 

 Germany. 



The only authors who have hitherto described and figured the species are Dr. Geinitz 

 and Professor King; 1 but I entirely coincide with Mr. Howse 2 and M. De Koninek, 



1 In the ' English Permian Fossils,' p. 85, Professor King makes use of the name Discina spelunearia 

 in preference to that of Koninckii. 



2 'Annals and Mag. of Nat Hist.,' vol. xix, 2d series, p. 44, 1857. 



