26 BRITISH CARBONIFEROUS BRACHIOPODA. 



unequal, bifurcated, or intercalated ribs, of which from ten to twelve occupy the surface of 

 the mesial fold and sinus. The following are the measurements from two examples : 



Length 28, width 36, depth 23 lines. 

 22, „ 30, „ 13 lines. 



Obs. I have been able to examine very few examples of the present form, but these 

 varied considerably both in degree of convexity as well as depth. The mesial fold is never 

 much elevated, and is at times scarcely defined, as in PI. VII, figs. 1 and 3 ; so that some 

 examples show hardly any frontal wave. The ribs also vary much in their respective 

 widths, even on the same individual, so much so that some specimens seem hardly dis- 

 tinguishable from Sp. bisulcata, while others approach most to Sp. duplicicosta ; it seems 

 however, to be much more regularly oval than is commonly the case with Phillips's species, 

 in which the mesial fold is also generally more elevated, giving to the shell a different 

 aspect. From Sp. bisulcata it seems distinguished by the shortness of its hinge-line. 



Loc. Dr. Griffith's examples are from the lower limestone of Mullaghfin and Milverton, 

 in Ireland. A fine specimen in the Cambridge Museum is labelled Derbyshire. It is not 

 very rare at Vise, in Belgium, whence Professor De Koninck's types were derived. 



Spirifera pl an ata, Phillips. Plate VII, figs. 25 — 36. 



Spirifera planata, Phillips, Geol. of Yorkshire, vol. ii, p. 219, pi. x, fig. 3, 1836. 

 Brachythyris planata, M'Coy. Synopsis of Carb. Foss. of Ireland, p. 146, 1844. 

 Spirifer rotundatus 1 Semenow (non Martin). Ueber die Fossilien des Schlesiscken 



Kohlenkalkes, 1854. 

 — recurvatus, M'Coy (non Be Koninck). British Palaeozoic Fossils, p. 421, 

 1855. 



Spec. Char. Almost circular or ovato-subtrigonal, often as wide as long; hinge- 

 line shorter than the width of the shell ; area triangular, of rather small dimensions. Dorsal 

 valve moderately convex, uniformly so in young and even aged individuals, so that 

 there hardly ever exists a regularly defined mesial fold, its position being in general 

 indicated by two deeper sulci. The ventral valve is much deeper and more convex, with 

 a narrow longitudinal sinus, producing but a slight frontal wave ; beak prominent and 

 incurved. The surface of the valves are ornamented by numerous delicate radiating ribs, 

 four or five occupying the place of the fold, while from thirteen to fifteen exist on either 

 side, several of which being due to intercalation at various distances from the beaks. 



Length and width rarely exceeding 9 or 10 lines, depth from 5 to 6 lines. 



Obs. This pretty little shell is a well-characterised and readily recognisable species, 

 but from not having been sufficiently described in the ' Geology of Yorkshire,' has given 

 rise to some false identifications, not only abroad but likewise at home; for in the 



