n SPIRIFERA. 29 



in character between Martin's specimen and that figured by Professor M'Coy. The 

 number of ribs also varies a little in different individuals. 



This shell was well described and figured in 1843 by Professor De Koninck, in his 

 excellent work on Belgian Carboniferous fossils, and through that gentleman's kindness 

 I have been able to examine the very few individuals he could obtain from the quarries 

 of Vise. M. De Koninck states that " this shell, whose denomination sufficiently denotes 

 the shape it usually assumes, is, above all, characterised by the singular conformation of 

 its sinus, to which no attention has been paid by the authors who have described it. This 

 sinus is smooth, and presents nothing particular in young individuals ; but when they 

 have acquired half their growth, a small ridge appears, which becomes wider with age, 

 and is never absent in the numerous varieties under which this species presents itself, and 

 of which we have figured the most dissimilar shapes," &c. 



The surface of the valves is ornamented, in addition to the ribs, by numerous concen- 

 tric lines of growth, which become the more approximate as they approach the margin 

 of the valves. I have, through the kindness of Dr. Griffith and Professor Sedgwick, been 

 enabled to examine the original examples on which Professor M'Coy founded his Sp. 

 ornithorhyncha, and to compare them with Martin's specimen of T. triangularis. Professor 

 Phillips's figure, in the ' Geol. of Yorkshire,' vol. ii, pi. ix, fig. 12, is larger than any 

 example I have seen, and cannot be considered a characteristic representation of the 

 species. 



Loc. This shell was obtained at Buxton by Martin. It occurs also in Derbyshire ; 

 at Settle, in Yorkshire ; at Bolland, Kirkby Lonsdale, &c. Professor M'Coy's specimens 

 were from Millecent (Clare), Ireland. I have not seen any Scotch specimens. 



Spirifera trigonalis, Martin. Plate V, figs. 25 — 34; 35 — 37? 



Conchyliolites anomites trigonalis, Martin. Pet. Derb., tabl. xxxvi, fig. 1, 1809. 

 Spirifer trigonalis, Sowerby. Min. Con., tab. 265, fig. 1 (not 2 and 3), 1820. 

 Spirifera trigonalis, var. a, M'Coy. British Palaeozoic Fossils, p. 423, 1855. 



Spec. Char. Transversely trigonal ; hinge-line almost as long, or a little longer, than 

 the width of the shell, the lateral angles being either rounded off or acute, and slightly 

 prolonged. Area sub-parallel, of moderate width, and divided by a triangular fissure, 

 covered in part by a pseudo-deltidium. Beak rounded, moderately produced, and 

 incurved ; valves almost equally convex ; the mesial fold in the dorsal valve is elevated, 

 angular, and extended beyond the level of the lateral portions of the valve ; it is, in 

 general, divided by three principal ribs, of which the central one is at the same time the 

 largest and most extended. In the ventral valve the sinus is deep, and likewise divided 

 by three longitudinal ribs, the central one being (as in the dorsal valve) the most developed. 



