344 R. EtJieridge, Jun. — Contributions to PaJceontology. 



III. — CONTEIBTJTIONS TO CaEBONIFEKOUS PALEONTOLOGY. 



On some fukthek Undescribed Species of Lamellibranchiata 

 FROM THE Carboniferous Series of Scotland. 



By E. Etheridge, Jun., F.G.S. 

 (PLATE XII.) 



IN the July Number of the Geological Magazine, I described 

 certain new species of bivalve Mollusca from the Carboniferous 

 series of Scotland. These will now be found on Plate XII., 

 accompanied by three other well-marked forms from the same 

 formation, and which appear to me to be undescribed. In Messrs. 

 Young and Armstrong's Catalogue of the Carboniferous Fossils 

 of the West of Scotland^ is recorded a new species of Fteronites, 

 imder the specific name of P. jiuctuosus (Etheridge, MS.), a shell 

 so named by my father, but never yet described. P. fluctuosus is 

 specifically remarkable for its small size, and the absence of ribs 

 on the anterior side. The disposition and arrangement of the shell 

 ornamentation affords a good means of specific identification in 

 several of the Carboniferous species of Fteronites, as the following 

 synopsis will indicate : — 



Fteronites persulcatus, (McCoy ).^ Shell large, with the surface 

 covered with coarse, rugged, flexuous, irregular, slightly interrupted 

 ridges. 



P. semisulcatus (McCoy) .^ Posterior wing and anterior side of the 

 shell devoid of ribs, which are confined to the central portion of the 

 shell, where they are obtusely rounded, and vary from seven to eight. 



P. sidcatus (McCoy).* The wing and a portion of the posterior end 

 in this species are smooth ; the remaining portion of the shell, includ- 

 ing the anterior side, is " roughened by about thirteen or fourteen 

 rugged obtuse ribs." 



P. regularis (E. Etheridge).^ Here we have, as regards general 

 outline and form, a repetition of P. persulcatus (McCoy), but the 

 shell is smaller, and the ribs are even, flexuous, and equidistant, not 

 rugged or broken up. 



Such is the variation in ribbing amongst the larger species of 

 Carboniferous Fteronites ; aud if we now add the same characters of 

 the species about to be described, P. fluctuosus, the gradual gradation 

 and variation in surface ornamentation will be apparent. In this 

 species the wing and posterior end, instead of being plain, as in 

 P. sulcatus, are covered with ribs, whilst the anterior side is devoid 

 of such. 



Three other species of Fteronites are found in British Carboniferous 

 rocks, but as two of them are smooth, and the form of the third is 

 sufficient to distinguish it, they need not be here taken into account. 



1 J. Young and J. Armstrong, " On the Carboniferous Fossils of tlie West of Scot- 

 land," Trans. Geol. Soc. Glasgow, vol. iii., 1871. 



2 McCoy, Brit. Pal. Fos. p. 480, pi. 3 F. fig. 1. 



3 McCoy, Synopsis Carb. Fos. p. 81, pi. 11, fig. 32. 

 ■* McCoy, Synopsis Carb. Fos. p. 82, pi. 13, fig. 5. 



* R. Etheridge, Geol. Mag. July, 1873, p. 298. 



