PARALLELODON SQUAMOSUS. 139 



Abca fihbriata, Bronn, 1848. Nomencl. palseont., p. 94. 



— d'Orh., 1850. Prodrome paleont., vol. i, p. 134. 



— Armstrong and Young, 1876. Catal. Western-Scot. Foss., p. 53. 



— squamosa, Bigshy, 1878. Thesaurus Devonico-Carbonif'erus, p. 299. 



— — Etheridge, 1885. Brit. Toss., part 1, Palaeozoic, p. 280. 

 Paeallelodon fijibeiatus, de Koninck, 1885. Annales Musee Hist. Nat. 



Belgique, vol. xi, p. 155, pi. xxiv, figs. 44, 45. 



Specific Characters. — Shell of only moderate size, transversely subquadrate, 

 obliquely swollen. The anterior end is short, compressed; its border almost 

 straight above, where it makes a rounded right angle with the hinge-line, and 

 semicircularly curved below, where it joins the inferior border, which is gently 

 rounded, with its convexity downwards. The posterior border is almost straight, 

 obliquely truncate (de Koninck). The hinge-line is straight, about as long as the 

 greatest transverse diameter of the shell. The umbones are small, pointed, non- 

 contiguous, but close ; raised above the hinge-line, and situated in the anterior 

 fourth of the hinge-line. Between the umbones is a well-marked, deeply sunk 

 ligamental area, striated longitudinally. The valves are moderately swollen above 

 and obliquely from the umbones to the posterior inferior angle, flattened below, 

 and much compressed and expanded at the posterior superior angle. 



Interior. — The details of the muscle-scars are unknown. The hinge consists of 

 a few small teeth in front, placed obliquely from above downwards and backwards, 

 and two very fine linear teeth posteriorly. 



Exterior. — The surface is raised into a few (eight to twelve) concentric 

 lamellae, which are convexly swollen from above downwards, and have their lower 

 borders imbricating. These folds are separated by concentric V-shaped grooves, 

 and become wider as they pass from the front to the posterior part of the 

 valve. There is an obscure angulation in the folds where they become bent 

 upwards to reach the superior border. The folds and grooves appear to be quite 

 smooth, without any trace of radiating lines. 



Dimensions : 



Antero-posteriorly. Dorso-ventrally. Elevation of valve. 

 PI. IX, fig. 19, measures 18 mm. (estimated) 13 mm. 5 mm. 



Localities. — England : The Carboniferous Limestone of Settle and Hill Bolton, 

 Yorkshire ; Wetton, Staffordshire. 



Observations. — Parallelodon squamosus is a very easily distinguished species, 

 differing decidedly in shape and ornament from all other species of the genus. 



Originally described by de Koninck {op. supra cit.) as Area squamosa, the 

 specific name was altered to A. fimbriate/,, in the Appendix, for reasons of 

 nomenclature. Incidentally in the same vearM'Coy adopted the same name for a 



