ALLORISMA MONENSIS. 427 



of fair size, eloDgate. The escutcheon is well developed, deep, broad, and long, 

 marked off from tlie rest of the valve by an angular ridge parallel to the hinge- 

 line. 



Interior. — The anterior adductor muscle-scar is large, oval, and shallow ; 

 marginal, bounded, as in the genus Sanguinolites, by a curved ridge behind. 

 Tlie posterior adductor scar is large, ovate, and shallow, placed close to the 

 hinge-line, but very remote from the posterior end. The pallial line is markedly 

 sinuate, remote from the margin. The hinge-line is edentulous, with a rolled 

 margin posteriorly. 



The inner surface was marked by broad, shallow, concentric grooves and 

 rounded ridges, crossed by very obscure, almost obsolete, radiating lines. Im- 

 mediately below the point where the valves are bent on themselves to form the 

 escutcheon there is to be seen in casts a broad compression parallel to the hinge- 

 line. 



Exterior. — The shell is ornamented witli many fine concentric strige and 

 wrinkles, obscurely collected below into grooves and ridges, which become much 

 more apparent in the neighbourhood of the broad sulcus. The dorsal slope is 

 smoother, and crossed by at least one radiating line. Shell very thin. 



Dimensions. — PI. XLYII, fig. 12, measures — 



Antero-posteriorly . . . .73 mm. 



Dorso-ventrally . . . .38 mm. 



From side to side . . . .30 mm. 



Localities. — England : the Lower Limestones of Scarlett Point and Balasala, 

 Isle of Man. Ireland : the Carboniferous Limestone of Donaghrisk and Carnteel, 

 CO. Tyrone. 



Observations. — This species is found in the Lower Limestones of the Isle of 

 Man with Edmondia sulcata and Prolecanites compressus (Sow.), the Goniatites 

 Henslowi of the same author. Judo-ing' from the close resemblance between the 

 fauna of the limestone of Kendal Fell, Westmoreland, and that of the Lower 

 Limestones of the Isle of Man, I think it most likely that this species will be found 

 there also. A. mone^isis resembles A. Ansticei more closely than any other species 

 of the genus, but its anterior end is comparatively much shorter and deeper, the 

 valves much less gibbose, and the dorsal slope more compressed and less hollow. 

 The surface-markings are also much stronger. 



I have referred three very imperfect casts from Donaghrisk, co. Tyrone, 

 to this species. They are preserved in the collection of the Geological Survey 

 in the Science and Art Museum, Dublin ; and there is an undoubted specimen 

 from Carnteel, in the same county, in the collection of the Q-eological Survey at 

 Jermyn Street. 



