SPIRIFERA. 35 



Spirifera convoluta, Phillips. Plate V, figs. 2 — 15. 



Spimfeka convoluta, Phillips. Geol. of Yorkshire, vol. ii, p. 217, pi. ix, fig. 7, 183G. 



— khomboidea, Phillips (?). Ibid., figs. 8, 9. 



— convoluta, De Eoninck. Animaux foss. de la Belgique, p. 247, pi. xvii, 



fig. 2, 1843. 



— — M'Coy. Synopsis of Carb. Foss. of Ireland, p. 130, 1844. 



Spec. Char. Fusiform, three or four times as wide as long, with a straight hinge-line, 

 to which the lateral margins of each valve rapidly converge, producing acute angles at the 

 extremities. Area rather narrow, and parallel-sided, with a triangular fissure partly covered 

 by a pseudo-deltidium. Beak small, and but slightly produced beyond the cardinal edge. 

 Ventral valve a little more convex than the dorsal one, with a sinus of variable depth and 

 width, and which corresponds in the small valve with a mesial fold at times considerably 

 elevated above the general convexity of the valve, and to which is due the strong frontal 

 wave observable in some examples. Each valve is ornamented by from thirty to forty 

 simple or intercalated ribs of unequal width, three or four of which occupying the mesial fold 

 and sinus. Full-grown examples measured — 



Length 11, width 45, depth 9 lines. 

 „ 14, ,, 36, „ 15 lines. 



Obs. This species is easily distinguished from other Carboniferous Spirifers by its 

 great width compared to its length, which gives to the shell much the appearance of a 

 weaver's spindle. The ribs in adult individuals are often much contorted and irregular 

 in their width, as may be seen in specimens figs. 9 and 12. Professor Phillips 

 represents a specimen in which one of the wings was imperfect. This I have 

 replaced in the more correct illustration of the same example, fig. 9 j here, as in fig. 1 2, 

 the mesial fold has but little elevation above the general convexity of the valve ; but in 

 another of Professor Phillips's type specimens in the British Museum, as well as in one 

 (figs. 14 and 15) belonging to the Royal Dublin Society, the mesial fold is considerably 

 elevated. Professor De Koninck has published a very good description and illustration 

 of this species, and mentions that in the young specimens the shell is far from pre- 

 senting so extreme a transverse shape as it afterwards assumed. The lines of growth on 

 the specimens from which figs. 9 and 12 were drawn denote that, while the length was 3^ 

 lines, the width did not exceed 9, and others seem to have been still less transverse. 

 Professor De Koninck is also of opinion that 8. rhomboidea (figs. 2 — S) and 8. fusiformis, 

 Phillips, cannot be considered distinct from 8. convoluta, and proposes to place both names 

 among the synonyms. Having been able to study numerous examples of 8. rhomboidea, 

 I feel disposed to agree so far with my learned friend, while refusing to the last-named 

 shell a separate specific value. The name may, however, perhaps be retained as a varietal 

 denomination for 8. convoluta, in which the ribs on the mesial fold are less defined than on 



