PROTOSCHIZODUS ^EQUILATERALIS. 247 



oblique from above downwards and backwards. The postero-inferior angle is 

 almost a right angle, but the postero-superior angle is obtuse. The hinge-line is 

 arcuate in front, but produced and straight posteriorly, and somewhat depressed 

 downwards. 



The umbones are of moderate size, marked off both in front and behind by a 

 distinct fold, and twisted forwards, pointed, incurved, contiguous, raised above 

 the hinge-line, and situated in the anterior third of the valve. 



Proceeding downwards and backwards from the posterior border of the umbo 

 to the postero-inferior angle is a more or less acute ridge, posterior to which the 

 shell is rapidly compressed and somewhat expanded. There is a second ridge 

 close to the hinge-line, formed by the bending of the valve on itself to form the 

 hinge-plate, which is fairly constant, and gives rise to a pseudo-escutcheon. 



Interior. — The anterior adductor muscle-scar is subcircular ; its position is 

 high up, and just within the anterior edge of the valve. The posterior is placed 

 high up on the dorsal slope, and very inconspicuous. The pallial line is entire, 

 and remote from the margin. The hinge has not yet been exposed. 



Exterior. — The surface is almost smooth, but under the microscope fine 

 concentric lines, parallel to the margins, are to be seen, and these become a little 

 coarser or subimbricating as they pass over the posterior slope to end in the 

 hinge-line, and are fairly well marked at the lower margin. Shell thin. 



Dimensions. — Fig. 5, PL XX, from Magazine Limeworks, Pathhead, measures — 



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



48 mm. 41 mm. 10 mm. 



The type of M'Coy's ^ 



■nii -7 . 7 - £■ .35 mm. 4- (not perfect) 37 mm. — 



JJolabra seqailateralis ) ' v r ' 



Localities. — Ireland: the Carboniferous Limestone; Clonmel ; Monaster; 

 Doorin, Co. Donegal; Limerick. Scotland: Magazine Ironworks, Pathhead; 

 Burn Anne ; Calderwood Cement-stone, East Kilbride. 



The type-specimen of Dolabra sequilateralis, M'Coy, is very poor and incom- 

 plete, it has lost a good deal of the posterior end, and the umbo is badly pre- 

 served. On this account it is a very unsatisfactory specimen on which to found a 

 species, and the drawing given by M'Coy is largely ideal. In its incomplete 

 condition this type does not appear to be so oblique as the shells which I have 

 ventured to think belong to M'Coy's species ; and the original shell, now pre- 

 served in the Griffith Collection in the Science and Art Museum, Dublin, is here 

 refigured. Mr. R. Etheridge, jun., described and figured a certain specimen from 

 the Calderwood cement-stone as Leptodomus fragilis (op. cit.), which, from its 

 obliquity and the angular nature of the oblique ridge, cannot belong to that 

 species ; but which I have no doubt is the same species as the shell here figured, 

 PI. XX, fig. 5, from Pathhead. A comparison of this specimen with the type 



