302 EJdTISH SILURIAN BRAClilOPODA. 



of its sculpture, which is closer and finer in some examples than in others. To the more 

 closely striated and corrugated varieties (fig. 8) Portlock gave the name of corrugata ; and 

 M'Coy that of undulata to those specimens in which the ribs are fewer in number and 

 the interspaces consequently wnder (fig. 14). These extremes are, however, intimately 

 connected by examples possessing every intermediate character. It will be necessary to 

 alter the termination of Portlock's specific designation of corrugata to that of corrugatella 

 if we desire to preserve the memory of his w^ell-known name ; for shortly before 1843 the 

 term Strophomena corrugata had been applied by Conrad to an American shell specifically 

 distinct from that of Portlock, in the 'Journ. Acad. Nat. Sci. Philadelphia,' vol. viii, 

 p. 256, pi. xvi, fig. 8; and again by J. Hall in his ' Geol. Report Fourth District New 

 York,' p. 73, fig. 2, 1843. The designation ^'undulata" had also been given by Vanuxem 

 to a variety of Stropkomena rhomboidalis previous to the publication of M'Coy 's descrip- 

 tion (' Geol. Report Third District New York,' p. 139, fig. 3, 1842 ; see also J. Hall's 

 ' Palaeontology of New York,' vol. iii, p. 19(5). 



In external shape and sculpture this shell also nearly approaches to Leptcena or Stropho- 

 mena interstrialis and Stroph. nobilis (M'Coy) from the Middle Devonian Rocks of Devon- 

 shire ; but this last appears to be a larger and more convex shell ; but it may possibly be 

 only a modification of the Silurian form (in the Darwinian point of view) ; and it is highly 

 probable that, when more completely known, this may be found to be the case with many 

 forms which we are at present unavoidably compelled to regard as distinct. There can 

 be little doubt that future Palaeontologists, with a more extended knowledge derived from 

 the labours of their predecessors, will be able to reduce the number of so-termed species. 

 To attempt too much at present, however, with these incompletely known shells would 

 render us liable to err in the opposite direction. 



Position and Locality. Stropkomena corrvgatella is at present known only from the 

 Llandeilo and Caradoc formations. 



In the Llandeilo at Goldengrove and Merigomish, Llandeilo District. 



In the Carodoc at Keisley, near Appleby (Westmoreland). This locaHty, according 

 to Prof. Harkness, is the equivalent of the Bala or Coniston Limestone, or Middle 

 Caradoc, and corresponding to that of the Chair of Kildare. 



It is also stated by Phillips and Salter to occur at Craig-y-Garcyd in the Usk District, 

 and at Gwm Craig-ddu, near Builth. 



In Scotland it has been found at Balclatchie and Penkill, near Girvan, in Ayshire. 



In Ireland in the Caradoc of Deserccreat (Tyrone) ; the Chair of Kildare ; Newtown 

 (Waterford) ; Grangegeeth (Kerry), &c. 



Abroad it is mentioned by Barrande from Bohemia, &c. ; but we must be careful not 

 to confound it with the Sir. corrvgata of Conrad, to which D'Eichwald and some other 

 authors refer. 



