11 
Localities and Ilonzon . — Cessiioek {C. C alien) ; Portion 97, Parish 
Milfielcl, County Nortbumherlancl {C. Callen). — Permo-Carboniferous — Upper 
Marine Series. 
Collection . — Minimr and Gcoloi^ical Museum. 
O O 
Aviculopectex Mitciielli, s}). nov. 
(Plate T, Figs. 1-3 ; PI. IJ, Fig. 1 ; PI. X, Fig. .5 ; PI. XII, Fig. ; PI. XllI, Fig. 3 ; PI. XVJ, 
Figs. 2, 3.) 
Specific Characters. — Shell longitudinally oval ; valves unequally bi- 
convex ; aurieles very similar in both valves. Left valve tlie more convex, 
and tumid; umbo acute, larger than that of the right valve, and raised 
slightly above the cardinal margin ; anterior and posterior slopes very 
pronounced. Eight valve gently convex, becoming Hatter towards the 
ventral margin. Anterior auricles of both valves triangular, moderately 
large, the outer edges rounded, and a byssal sinus Ijelow that of the right 
valve ; posterior auricles small, rectangular, flattened. Costa' comparatively 
few i)i number — twenty to twentj^-two — of one order and simple, subangular, 
with broad, rather concave intercostal spaces, or valleys, the whole crossed 
by strong, close, concentric, wavy frills or laininm ; the posterior and 
anterior auricles are coarsely costate. 
Observations. — We have several s])ecimens of this large and very tumid 
valve from the AVest Maitland District, but unfortunately none are perfect. 
It is, however, so marked a form, and so eminently characteristic of the 
Lower Marine deposits, that it cannot be passed over in silence. AYe believe 
it to be the — 
1. Fecten illawarrensis, Dana.’ — The figure represents a large convex 
valve, but Dana states that both valves are so, and with eighteen to twenty 
costate ; auricles large. 
2. Aviculopecten illawarensis, De Koninek.'“ — This author tigured a 
shell with the valves in apposition, and refers to the simplicity of the costm, 
but in bis illustration some of these are unquestionably bifurcate. It was 
inequivalve, Avitb mutilated auricles, eighteen to twenty costae, and the left 
' Dana — Wilkes U. S. Explor. Exped., 1349, X (Geol.), p. 705, t. 9, f. 9, 9.t. 
' Pe Koiiinck — Pvech. Foss. Pal. Xouv.-Galles Ju Sud, 1877, pt. 3, p. 163, t. 22, f. 1 
