269 
Loc. and Horizon. West of the Dividing Eange, at the Crow’s Nest, Mount 
Victoria, near Mount Morgan {The late James S?>iith ; Mining and Geol. Mus., 
Sydney) ; Eoohhampton District* {G. W. Te Vis ; Colin. De Vis) — Gympie Beds. 
Genus — TVLTOPECTEN', gen. nov. 
Gen. Char. Shell possessing the general structure of Avicuhpecten, hut the 
valves very inequivalve, the larger or convex valve with a high overcurved umbo, 
overhanging a long triangular hinge area, with longitudinal cartilage furrows, and a 
large deltoid-triangular cartilage pit. 
Ols. Deltopecten is iutorinediate in its structure between Pecten and 
Aviculopecten. It jDossesses the central cartilage pit of the former, and the furrowed 
area of the latter, and besides this the larger or convex valve is much higher 
than its neighbour, the umbo of the one overhanging that of the other, similar to the 
structure of the genus Janira. It may therefore be said to be a compound of the 
structure of all three genera. This so thoroughly departs from the structure of 
Aviculopecten, and is, further, such an additional modification of the hinge structure in 
this group of shells, to that indicated of late by various American Authors, that it seems 
to me to bo worthy of generic distinction. I therefore propose for the following 
Australian species, the only one in which I have as yet noticed this structure, the 
name Deltopecten, in allusion to the shape of the cartilage pit or depression occupying 
the hinge area. 
Type. Pecten illawarensis, Morris. 
Deltopecten illxwaeensis, Morris, sp., PI. 41, fig. 3 ; PI. 43, fig 2. 
Pecten illawarensis, Morris in Strzelecki’s Phys. Descrip. N. S. Wales, &c,, 1845, p. 277, t. 14, f. 3. 
„ „ Dana, Geology Wilkes’ U. S. Explor. E.xped., Vol. x., 1849, p. 705, Atlas, t. 9, f. 9. 
.Aviculopecten illawarensis, De Koninck, Foss. Pal. Nouv.-Galles du feud, Pt. 3, 1877, p. 301, t. 22, f. 1. 
Ols. Prof. De Koninct has correctly described this shell as inequivalve, even 
allowing for the fact tliat nearly all shells of this group are more or less so. The 
larger valve is very much the more convex of the two, and better developed, with a large 
and high umbo overhanging the hinge area. These points are well shown in De 
Koninck’s figures. The area is exceedingly broad and strong, especially beneath the 
umbones, w^here it is excavated into a pseudo-cartilage i)it of a deltoid or roundly 
triangular form, the area gradually narrowing outwards towards the anterior and 
posterior extremities. The pit must have been the receptacle for a large and strong 
cartilage. The whole area is coarsely transversely striated, or grooved. 
The radiating cost® of the surface vary to some extent in number. In Prof. 
Morris’s figure, which appears to be that of the smaller valve, there are twelve or thirteen 
ribs, in that given by De Koninck of the same valve fifteen, whilst his view of the 
convex valve exhibits still more, perhaps twenty. In our specimens, the average 
number appears to bo about fourteen. 
The depression of the valves towards the front margins, referred to by De 
Koninck, takes place between the edges and the pallial impression, which is a well- 
niarked feature in the examples before me. 
In Professor James Hall’s figure of Aviculopecten princeps, Conrad, sp.,t there 
is both a triangular area, and a central depression. The former is very apparent, 
* See note, p. 199. 
+ Prelim. Notice Lamellib. Shells, Up. Helderberg, 
Hamilton atirt Chemung Groups, Pt. 1, 1884, 
