222 BRITISH CARBONIFEROUS BRACHIOPODA. 



Spirifera trigonalis, Martin. 



At one time I erroneously believed, with the generality of Palaeontologists, that 

 Sp. trigonalis, Martin, p. 29 ; Sp. bisulcata, Sow., p. 31; Sp. crassa, de Kon., p. 25 ; Sp. 

 grandicostata, M'Coy, p. 23 ; and Sp. transients, M'Coy, p. 33, were sufficiently distinct 

 to be retained as separate species; but a subsequent examination of a more extensive series 

 of specimens has led me to infer that they are all modifications of a single very variable 

 species, for which the term trigonalis, or bisulcata, should be retained ; and I am glad to 

 say that this opinion has been already accepted by several experienced observers. No 

 species is more variable in its general aspect,, or in the number of its ribs, still every 

 intermediate form may be found in our carboniferous limestone districts. To attempt, 

 therefore, to describe all these variations would be endless ; but the following figures will 

 convey an idea of its more prevalent shapes. We would therefore refer to Sp. trigonalis, 

 PI. IV, figs. 1, 2; PI. V, figs. 1, 23, 24, and 38, 39; PI. VI., figs. 1-22; PI. VII, 

 figs. 1 — 4, 7 — 16 ; and PI. L, figs. 3 — 8 ; but I am at the same time ready to allow that 

 if, for example, we take the winged more simple form, PI. L, fig. 7, and then compare it 

 with the transversely oval, rounded, thickened var. crassa (PI. VI, fig. 20), the notion of 

 both being modications of a single species will, to the generality of observers, appear 

 absurd ; still if we find every variations connecting these extremes, are we to refuse the 

 evidence of our eyes and senses, and to create as many species as we possess specimens ? In 

 many examples of undoubted Sp. trigonalis and S. bisulcata, the cardinal angles are rounded 

 so that the hinge-line is shorter than the breadth of the shell, but in the larger number of 

 individuals these angles became more or less prolonged, and in some specimens they form long 

 attenuated wings (PI. L, figs. 3, 5, 6, 7, 8, and 9). In his list of the carboniferous Brachio- 

 poda of Belgium, Prof, de Koninck admits that his Sp. crassus, and M'Coy's Sp. grandi- 

 costata are in all probability varieties of Sp. bisculata} In its most simple shape, the 

 sinus of S. trigonalis presents three longitudinal ribs, of which the central one is usually 

 the largest (PL L, figs. 3 and 7) ; in other specimens there exists five, or two smaller ones, 

 one on either side of the central rib (fig. 4), while in larger individuals we often find seven 

 ribs, or three on either side of the central one (fig. 9), but in some specimens the ribs are 

 more numerous and less regular in their respective widths. The mesial fold is often com- 

 posed of three bifurcated ribs, or is divided by two sulci; but here again, although this is 

 certainly the prevalent feature, in some srjecimens these three ribs are more divided and 

 the fold is sometimes not so sharply bisulcatcd. The shell of Sp. trigonalis is but rarely 

 perfectly preserved, but when so the whole surface or ribs are finely striated and closely 

 imbricated or decussated "by numerous transverse fine spinulose or serrated ridges, as many 



1 ' Mcmoire sur les genres et les sons-genres des Brachiopodes munis d'appendices spiraux,' par M. 

 Davidson, traduit et augmcnt6 de Notes par le Dr. L. A. Koninck. ' Memoirs de la Societ6 Royale de 

 Liege,' 1859. 



