R. Mheridge, Jun. — Contributions to PalcBontology. 345 



They are P. angustatus^ (McCoy) ; P. latus^ (McCoy) ; and P. ventri- 

 cosus^ (McCoy). 



Pteronites fluctuosus unites, in the disposition of its shell ornamen- 

 tation, McCoy's two species, P. semisulcatus and P. sulcatus. It 

 agrees with the first-named in the comparative smoothness of the 

 anterior side, but departs from it in the possession of ribs on the 

 posterior side and wing, which likewise distinguishes it from the 

 last named, in addition to the anterior ribs of that species. The 

 specific diagnosis of P. fluctuosus is as follows : — 



Pteronites fluctuosus, sp. nov., PL XII., Fig. 1. 

 P. fluctuosus (Etheridge, MS.), J. Young and J. Armstrong's Cat. 

 Carb. Foss. W. Scotland, Trans. Geol. Soc. Glasgow, vol. iii., 

 1871, p. 48. {Without desc^-iption.) 



Specific char. — Transversely trigonal, slightly gibbous ; anterior 

 side rounded ; posterior end broad, somewhat sigmoidal ; posterior 

 wing rather large, thin, pointed, and, as indicated by the lines of 

 growth, reaching quite as far as the posterior side ; hinge-line 

 straight, well pronounced ; postero -ventral margin convex ; antero- 

 ventral margin concave ; beaks large, convex, nearly terminal ; 

 surface characteristically ornamented ; the posterior wing is marked 

 with equidistant, straight, strong, radiating ribs ; on the body of the 

 shell these become depressed, broad, and flexuous, passing down 

 towards the ventral margin ; beaks and anterior end of the shell are 

 comparatively plain, with the exception of a few lines of growth ; 

 lines of growth generally well marked, about five or six, distinctly 

 indicating the pointed nature of the wing. This shell is usually 

 found with the wing somewhat broken, as shown in the figure, re- 

 sulting probably from the delicacy of the shell. 



Localities. — Shale of the Lower Limestone Series, Craigenglen 

 Campsie. Discovered by Mr. J. Young, who has presented specimens 

 to the Museum of Practical Geology, London. 



One of the more interesting groups of shells found in Carboniferous 

 rocks is that of the Aviculopectinidce. Making its first appearance in 

 strata of Devonian age, Aviculopecten rapidly increased in specific 

 importance until in the succeeding Carboniferous the genus attained 

 its greatest development. From beds of this age in the British Islands 

 alone no less than about ninety-four species have been described. 

 It is, however, more than probable that many of these so-called 

 species are only the corresponding valves of forms described under 

 another specific name. In his " British Paleeozoic Fossils," McCoy 

 remarks that although the generality of the shells originally referred 

 to Pecten in Palfeozoic rocks would fall into his Avicidopecten, still, 

 this would not altogether preclude the occurrence of Pecten, and in 

 support of his argument cited a few species which he considered bore 

 out his views. In addition to those mentioned by McCoy, I have 

 evidence to show that several more of our Carboniferous Pectinoid 

 shells possess the characteristic central cartilage-pit in the hinge, 



1 McCoy. I.e. p. 81, pi. 13, f. 6. ' Bid. pi. 13, f. 7. ^ Ibid. pi. 13, f. 8. 



