APPENDIX. 337 



to make out any distinctive features ; and I found that Mr. Salter himself did not fail to 

 observe that his variety is not to be distinguished from the other " except by the shape of 

 the front edge, which is rounded off, and not squared at all." This last character, however, 

 cannot be considered of any importance, for I have before me specimens of L. ferruginea 

 of a similar size, which have the front quite as much rounded oflF as in the single example 

 of the var. ovalis. 



There can also be no doubt as to the shell termed L. unguiculus (in 1865) being the 

 same species as L. ferruginea described in 1867. Z. ferruginea, it is true, like most of 

 its congeners, varies slightly in its shape in different examples ; some having their front 

 a little more rounded than others, and the posterior portion converging rather more in 

 some individuals than in others. 



Position and Locality. After a very close study of a number of specimens submitted 

 to my examination by Messrs. Hicks and Belt, it appeared to me that the Lingulella 

 under notice made its first appearance in the lowest beds of the Harlech period, and 

 continued to live during the whole of the " Msenevian" or " Lower Llandeilo,'' and was 

 very probably, if not certainly, still existing during the period of the deposition of the 

 Middle and Upper Lingula-flags ; for several examples much resembling Salter's species 

 were met with by Mr. Belt in his " Dolgelly'' and other divisions. This, however, must 

 still remain an undecided question, for several specimens of Lingulella lepist^w hardly be 

 distinguished from L. ferruginea ; and in this predicament we find the small specimen 

 found by Mr. Hicks at Rhyw-felyn, near Mawddach, North Wales. L. ferruginea occurs 

 in the "Msenevian" rocks of St. David's, South Wales; as well as at Camlan, Tafern 

 Helig, Waterfall Valley, near Maentwrog, and several other places in North Wales ; also 

 in the Harlech Grits of Solva and St. David's. 



Genus — Lingula. 

 (See ' General Introduction,' p. 13J.) 



Lingula petalon, Ilicls. PL XLIX, fig. 30. 



Lingula petalon {Sicks, MS.), Dav. Geol. Mag., vol. v, p. 308, pi. xv, fig. 16, 



]8G8. 



Spec. Char. Shell small; broadest about the middle, and then becoming rapidly 

 and obtusely rounded. Valves much flattened, and marked by concentric lines of 

 growth. 



Length 5, width 4^ lines. 

 Ohs. Well authenticated species of Lingula do not appear to have been discovered 



43 



