65 
side is slightly arched, so that an antero-posterior section is represented by a 
sigmoidal line, while the transverse shows a line slightly hnt uniformly 
curved. The fissure, of which the anterior extremity commences almost at 
the central point, is oval, elongate, and rather narrow. All the exterior 
surface is covered hy fine concentric vertical lamellEe, separated from one 
another by furrows a little broader than the lamelhe, and al)out fifty in 
number. 
Dimensions. — Antero-posterior diameter, forty millimetres ; transverse 
diameter, thirty-four millimetres ; width of the fissure, two millimetres. 
Delations and Differences. — In size and ornamentation this sj)ecies 
resembles Discina glehosa, de Eyckholt, which this author has classed with 
Delcion, with which it has no relation. It differs from it in its more rounded 
shape and in the greater number of concentric lamellte. 
Horizon and Localities. — A single specimen of this species has been 
collected in the black Devonian limestone from the neijjhbourhood of Yass. 
The same piece of stone contains a rather well exposed specimen of Murcliisonia 
angulata, d’Archiac and de Verneiiil. Mr. J. Hall discovered it in the 
Chemung Group at Ilobbieville, Alleghany County, New York State. 
STROPHALOSIA, King. 
Stropiialosia productoides, Ilall. 
Ortllis productoides , Murcbison, 1840, Bull. Soc. Geol. France, XI (1), p. 251, pi. 2, 
fig. 7. 
Lep)tcena caperata, J. de C. Sowerby, 1810, Trans. Geol. Soc. London, V (2), p. 701, pi. 53, 
fig. 4, and pi. 51, fig. 3. 
„ ,, J. Phillips, 1841, Pal. Foss. Cornwall, p. 58, pi. 25, fig. 98. 
D roductus ILurcllisonianus (partim), L. G. de Koninck, 1817, Eeclierches Anim. Foss., 
I, p. 138, pi. 16, fig. 3 (Jiff- excli). 
Stropiialosia productiodes, T. Davidson, ISGl, Mon. Brit. Brack., p. 97, pi. 191, fig. 13-25. 
Shell suborbicular or subsemicircular, hinge line a little shorter than the 
transverse diameter. V entral valve slightly but regularly arched, non-sinuate, 
ears obtuse, beak small and little prominent. iVrea rather narrow, slightly 
triangular, and provided with a faintly visible pseudo-deltidium. Dorsal 
