Vol. 65.] CARBONIFEROUS LIMESTONE OP COUNTY CLARE. 575 



The ventral valve is more convex than the dorsal. Ribs numer- 

 ous, rounded or slightly flattened. 



In the dorsal valve a median fold, bounded on each side by a 

 distinct groove, has its origin near the extremity of the beak ; 

 but it does not become prominent until it approaches the anterior 

 margin of the shell, where it is considerably elevated, with steep 

 sides, and bears usually about twelve ribs. The sides of the dorsal 

 valve in an adult shell are somewhat flattened, and each bears 

 about fifteen prominent ribs and numerous smaller ones towards 

 the cardinal angles. A few ribs on each side of the median fold 

 increase by bifurcation. 



The ventral valve possesses a prominent though shallow sinus. 

 In the young shell this is simple ; but, as growth proceeds, it tends 

 to be divided by a small median fold, formed by the fusion of four 

 or five ribs. 



In a well-preserved specimen the ribs are seen to be covered by 

 fine longitudinal stria?, crossed by obscure lines of growth which 

 give them a reticulated appearance. 



Discussion. — This shell, in general form, in the nature of its 

 ribbing, and in the finely reticulate surface, bears a close resemblance 

 to the Belgian species figured and described by L. G. de Koninck 

 as Spirifer cinctus, de Keys. 1 The fold, however, is stronger than 

 in the Belgian shell, and the double nature of the sinus seems to 

 be a distinct feature, although there is perhaps a suggestion of this 

 in fig. 7 [op. cit.). The ribs, too, appear to be less numerous and 

 not so flattened. 



De Koninck's interpretation of Spirifer cinctus seems to be open to adverse 

 criticism, for his figures and description bear little resemblance to those of 

 A. von Keyserling, the founder of the species ; see the latxer's ' Wissensch. 

 Beobaeht. auf einer Reise in das Petschoraland im Jahre 1843 ' St. Petersburg 

 1846, p. 229 & pi. viii, fig. 2. The original type of this author appears to be 

 readily distinguishable from all other Carboniferous Spirifers by the absence 

 of a median fold and sinus, and by the possession of a uniplanar valvular 

 intersection (op. cit. pp. 229-30) : — ' Der entschiedne Mangel eines Sinus 

 unterscheidet ihn von alien Arten auf das ausgezeichnetste. ... In Folge 

 dessen wird die Stirncommissur nicht so wie bei auderen Arten zur Ventral- 

 schale herabgedrangt, sondern liegt fast in derselben Ebene ringsum.' 



It is not easy to understand how de Koninck confounded with this species 

 a form having a strong fold and sinus 2 (see de Kon. op. cit. p. 108 : ' La 

 valve ventrale ... est deprimee dans sa partie mediane par un large sinus 

 correspondant au lobe de la valve opposee '). 



A form, somewhat similar to the Irish species and probably 

 representing a parallel stock, occurs in the Keokuk Limestone of 

 America, which appears to correspond to our Syringothi/ris Zone. 

 This species (Spirifer logani, Hall) is, however, rather more 

 transverse, and bears more numerous ribs. 3 Of British examples 



1 Bull. Musee Eoy. Hist. Nat. Belg. vol. ii (1883) pi. xv, figs. 3-5 ; and 

 Annales, ibid. vol. xiv (lb87) p. 108, pi. xxiv, figs. 6-7 & pi. xxvi, figs. 1-2. 



2 De Koninck records Spirifer cinctus from Ballydoole (County Limerick). 



3 ' Natural History of New York' : Part VI — Palaeontology ' vol. viii, pt. ii 

 (1894) pi. xxxii, fig. 7. 



Q. J". G. S. No. 260. 2 r 



