140 DEVONIAN FAUNA. 



2. Genus — Pleuronectites, Schlotheim, 1820. 

 (Streblopteria, M'Coy, 1851.) 



Shell subequivalve, oval or subcircular ; anterior side obliquely produced in 

 front ; hind wing large, confluent, with a right or obtuse terminal angle ; front 

 wings short, in the left valve defined by an oblique groove, and in the right indented 

 by a byssal notch ; surface smooth or finely radiated ; muscular scar faint and above 

 the centre ; hinge with a narrow oblique tooth in front of the umbo ; ligamental 

 groove simple and narrow. 



The above description iscondensedfrom De Koninck's definition of Streblopteria, 1 

 which is a genus w r ith the Carboniferous Meleagrina laevigata, M'Coy, 2 for its type. 

 Freeh 3 points out that it is synonymous with Pleuronectites ; and PI. laevigata, 

 Schlotheim, 4 of the Trias, which is the type of that genus, though differing 

 specifically, is evidently congeneric with M'Coy's species. 



1. Pleuronectites Piltonensis, n. sp. Plate XVI, figs. 7 — 9, 10?, 11 ? 



Description. — Right valve small, subovoid, broad, gently convex, more or less 

 oblique. Umbo small, acute, direct, rather flattened, hardly extending above the 

 hinge, and situated rather behind the middle. Hinge-line more than half the 

 length of shell. Anterior wing long, narrow, convex, ovate, marked by four or 

 five coarse low rays and some cross strias ; defined by a deep narrow groove, and 

 bounded by a semicircular margin. Posterior wing short, flat, obtusely triangular, 

 defined by a linear oblique groove. Anterior margin semicircular at the wing, 

 then with a deep, narrow, angular notch, and then spreading out in a broad, bluntly 

 subangular curve, which becomes subcircular below. Inferior margin narrow, 

 convex. Posterior margin neatly convex. Contour of back gently convex, 

 spreading out flatly to the margins. Surface apparently smooth (or only micro- 

 scopically marked). Muscle-scar very large, central, situated in the upper half 

 of the shell. 



? Left valve ovoid, more or less broad and oblique, rather convex. Umbo oblique, 

 acute, reaching slightly above hinge. Anterior wing small, flat, short, equilaterally 

 triangular, and marked with a few radiating and transverse lineations. Posterior 

 wing apparently small, short, flat, and very broad, more or less distinctly defined, 



1 1885, de Koninck, ' Ann. Mus. Boy. H. N. Belg.,' vol. xi, p. 202. 



2 1844, M'Coy, ' Syn. Carb. Foss. Ireland,' p. 80, pi. xii, fig. 5. 



3 1891, Freeh, ' Abhandl. Geol. Specialk. Preuss.,' Band ix, pt. 3, p. 12. 



4 1820, Schlotheim, ' Petref.,' vol. i, p. 217 ; and 1S50-56, Bronn, « Lethaea,' ed. 3, p. 161, pi. xi, 

 fig. 11. 



