PROTOSCHIZODUS MAGNUS. 245 



The specimen of an interior figured PI. XIX, fig. 12, shows that the pallial line 

 was entire. 



PftOTOSCHizoDus magnus, de Koninch, 1885. Plate XIX, figs. 22, 22 a, 23. 



Protoschizodts magnus, de Koninch, 1885. Arm. Mus. Hoy. Hist. Nat. Belgique, 



vol. xi, p. 12(5, pi. xiii, figs. 1 — 3. 



Specific Characters. — Shell of medium size, moderately compressed, triangularly 

 suborbicular, subequilateral, subalate at the postero-superior angle. The anterior 

 end forming rather less than half the shell, is produced forwards, and regularly 

 and gradually compressed into the margins. The anterior border, immediately 

 continuous with the hinge-line above, is only gently curved, passes forwards and 

 downwards, and then being bluntly curved backwards becomes the inferior 

 border, which is very convex, especially in front and behind. The posterior 

 border is truncate and nearly straight above, making a well-marked obtuse 

 angle ; below it becomes curved, and so joins the inferior border. The hinge-line 

 is short in front and curved; posteriorly it is straight, depressed, and produced. 

 The umbones are small, not marked off at all in front from the rest of the valve ; 

 pointed, contiguous, almost central, and not much raised above the hinge-line. 

 Posterior to a line passing from the umbo to the postero-inferior angle the valve 

 is rapidly compressed and expanded, so that the dorsal slope is concave. Else- 

 where the valves are regularly but slightly convex, and there is no indication of 

 an oblique ridge. The ligament is small and external, situated in a very narrow 

 groove posterior to the umbones. 



Interior. — This has not been well observed, but there are indications that the 

 muscle-scars are normal in position. Pallial line entire. 



Exterior. — The surface is ornamented with very numerous, regular, fine, con- 

 centric lines of growth, more apparent near the anterior edge. 



Dimensions. — Fig. 22, PI. XIX, measures — 



Antero-posteriorly . . . .53 mm. 



Dorso-ventrally . . . .47 mm. 



Laterally . . . . .23 mm. 



Localities. — Ireland : the Carboniferous Limestone of Ballyhomon, co. 

 Limerick, and Little Island, co. Cork. 



Observations. — I have met with only two specimens of this species, both of 

 which occurred in Irish beds ; one, a very fine testiferous example, is in the 

 collection of the Geological Survey of Ireland, and the other is in the cabinet of 

 Mr. Joseph Wright, F.G.S., of Belfast. These two shells are distinguished from 

 other species of the genus by their peculiar shape. The produced anterior end, 



