PROTOSCHIZODUS RECTANGULARIS. 237 



Peotoschizodus eectangulaeis, M'Coy, sp., 1844. Plate XVIII, fig. 20, and 



Plate XIX, figs. 2, 3. 



Dolabua eectangulaeis, M'Coy, 1844. Synops. Carb. Foss. Ireland, p. 6G, 



pi. xi, fig. 10. 

 — — Morris, 1S54. Cat. Brit. Foss., edit. 2, p. 202. 



CuculLjEA eectangulaeis, Bigsby, 1878. Thesaurus Devonico-Carbouif., p. 305. 

 Dolabea eectangulaeis, Etheridge, 1888. Brit. Fuss., vol. i, Palaeoz., p. 283. 



Specific Characters. — Shell triangularly gibbose, subquadrate, of moderate size 

 only, almost equilateral, much compressed and subalate posteriorly. The anterior 

 end is compressed and flattened from before backwards, and has its border 

 semicircularly curved. It is continuous "with the inferior border, which is 

 regularly convex downwards, meeting the posterior border at a w ell-marked, 

 slightly obtuse angle. The posterior border is almost straight, obliquely truncate 

 from above downwards and backwards, and it makes a well-marked angle with 

 the hinge-line above. The hinge-line is short and arcuate. The umbones are 

 small, acutely pointed, contiguous, only slightly raised above the hinge-line, and 

 subcentral. The umbonal swelling is well marked off, both in front and behind, 

 from the rest of the valve, and is triangular and regularly convex ; the anterior 

 border being regularly rounded, steep above, but gradually lost in its passage 

 downwards. The posterior umbonal border is very oblique and strongly sub- 

 angular, and is continued as far as the postero-inferior angle. Posterior to this 

 oblique ridge the valves are markedly and abruptly compressed, and somewhat 

 expanded, so as to be concave transversely. 



Interior. — The muscle-scars are normal in position, and the pallial line is 

 entire. The hinge has not been isolated. 



Exterior. — The surface is almost smooth, but fine concentric lines of growth 

 are to be seen towards the lower margin. Shell thin. 



Dimensions. — Fig. 20, PL XVIII, from Settle, measures — 



Antero-posteriorly . . . .32 mm. 



Dorso-ventrally . . . .28 mm. 



Elevation of valve . . . .8 mm. 



Localities. — England : the Carboniferous Limestone of Settle, Yorkshire. 

 Ireland : the Carboniferous Limestone of Firog and Ballyhomock, co. Limerick. 



Observations. — The type of M'Coy's species is a much smaller shell than those 

 here figured ; but he describes very exactly the characters of the shells which I now 

 refer to P. rectangularis. There is some curious misprint, I think, in M'Coy's 

 remarks on this species (op. cit., p. 60), as follows : — " This shell much resembles 

 the CucuUdea angusta, Sow., in general form, but is much more depressed, and is, 

 moreover, distinguished by its greatly larger beaks and prominent posterior 



