﻿STREPT0KI1YNCHUS. 



77 



Spirifer ? crenistria, Sow. Trans. Geol. Soc, 2nd ser., vol. v, pi. lvii, fig. 7 (read 



in 1840). 



Okthis ten uistkiata, Soiverby . Trans. Geol. Soc, 2nd series, vol. v, pi. lvii, 



fig. 12, 1840. 



— CMB ractjlum, Be Fern. Bull. Soc. Geol. de France, vol. xi, p. 253, 1840. 



— — De Fern, et D'Archiac. Trans. Geol. Soc, 2nd series, vol. vi, 



p. 396, 1841. 



Spirifer (?) crenistria (?) Phillips. Pal. Foss. of Cornwall, Devon, and West 



Somerset, p. 66, pi. xxvii, fig. 113, 1841. 

 Orthis crenistria, De Ferneuil et De Keyserling. Russia and the Ural Moun- 

 tains, vol. ii, p. 185, pi. xi, fig. 4, 1845 ; and De Keyserling, 

 Petschoraland, p. 221, pi. vii, fig. 7. 

 ■ — umbi! actjlum, Bronn. Index Pal., vol. ii, p. 861, 1818. 

 Lept.ena — M-Coy. British Pal. Foss., p. 388, 1852. 



— — Morris. Catalogue of British Fossils, p. 137, 1845. 



Orthisina crenistria, Sandb. Die Brach. des Rheinisclien Schichtensystems in 

 Nassau, p. 61, 1855. 



Spec. Cliar. Variable in shape, but usually transversely semicircular ; hinge-line straight, 

 nearly equal or slightly exceeding the width of the shell ; cardinal angles slightly rounded 

 or somewhat prolonged, with acute terminations ; area of the ventral valve variable in its 

 width, but divided by a convex pseudo-deltidium ; area of the dorsal valve linear. Dorsal 

 valve moderately convex, with sometimes a small mesial depression. Ventral valve slightly 

 convex, or so only near the beak, becoming gradually concave towards the margins, the 

 greatest width of the shell being about the middle. Surface of both valves covered with 

 numerous straight, radiating, slender, thread-like ribs, separated by slightly wider concave 

 interspaces, in the centre of which a shorter and smaller rib begins at variable distances 

 from the beaks, and extends to the front. The surface of the striae are more or less coarsely 

 and closely intersected with scale-like projections, while the interspaces are crossed by 

 finer and more numerous transverse lines of growth. Proportions variable — 

 Length 1 inch 9 lines, width 3 inches 4 lines, depth 5 lines. 



Obs. The interior details of the Devonian shell being similar to those of Str. crenistria, 

 as described at p. 125 of my ' Monograph of British Carboniferous Brachiopoda/ 1 it will 

 not be necessary to again repeat what has been already published. Much uncertainty has, 

 however, been entertained and expressed by several distinguished palaeontologists, with 

 reference to the specific value of Str. umbraculum and Str. crenistria, which some would 

 retain as separate species, but which others would combine under a single denomination ; 

 we will therefore enter upon some details, in order that the reader may be able to form 

 his own opinion on a question which may, perhaps, still claim a verdict of " not proven." 



In rocks of the Silurian age we find a shell with shapes and striation bearing resem- 



1 Figures of the interior of Streptorhynchus Devonicus, which agree in every particular with those of 

 St. umbraculum, may be seen in p. 29 of my 'Monograph of British Permian Brachiopoda.' 



