15 
a feature of the right valve of the Irish shell, in which, on the other hand; 
the costte are primary and secondary. Prom this it will l)e seen that the 
characters of the Irish and Australian forms, providing our reading of the 
above valve is correct, are exactly reversed. The auricles, although small, are 
highly radiate. In this unsatisfactory state we must leave the matter for 
further developments. 
Localities and Horizon . — Hills to west of Mount Uriari, Parish 
Somerton, County Parry ( C. Cullen) ; near Greenhills, Paterson [J. Waier-> 
house) . — Carboniferous. 
Collection. — Mining and Geological Museum. 
Aviculopecten Sphenti, Johnston. 
(Plato n, I-lgs. G and 7 ; PI. XIH, Figs. 1 and 9 ; PI. XVT, Fig.s. .5, G.) 
Aviculopecten Sjn'enlii, Julm.ston, Pim-. K. .Sue. Ta.s. fui- 188G (1887), p. 9. 
Avicnlopeclen Sprentii, Jolm.ston, Syst. Acc. (Jool. Tas., 1888, p. 115, t. 11, f. 11. 
Specific Characters. — Shell suhorhicular to fan- or scallop- shaped ; 
dorsal margin as long as the width of the shell ; ventral margin broadly 
rounded. Left valve gently convex ; anterior and posterior slopes rapidly 
converging to the umbo, which is sharp and pointed ; anterior auricle 
moderately large, triangular, the outer margin obliquely rounded, and 
emarginate only on uniting Avith the antero-lateral margin, and no defined 
byssal sinus ; posterior auricle large, battened, wing-like, very long, produced 
as far as the posterior extremity of the valve, acutely pointed at its posterior- 
dorsal angle, and with the outer margin deeply emarginate. Costm are 
primary, secondary, and tertiary ; the primary from ten to fourteen in 
number, strong, sharp, and angular ; the secondary occupy the centres of 
each intercostal space, Avith on each side of them a tertiary rib ; the anterior 
ear is multiradiate, and on the posterior there are at least four principal 
costm ; the Avhole valve is traversed concentrically in the first instance by 
latilaminae, in the second liy close frills, AA’hich, on passing over the primary 
and secondary costae, and on the auricles, rise into acute echinations (almost 
spines) at regular intervals ; there is also a prominent series of denticles 
along the dorsal margin, Hinge-plate linear. 
D 
