28 
The following arc the variations exhibited hy the costce, other than that 
described l)y McCoy : — 
(«) T)ic absence of tertiary costsc. 
(i) Two tertiary costtn between two primary to the exclusion of secondary, 
(e) Two tertiary costm on eaeli side of a secondary. 
AVe have only seen indifferent examph'S of the right valve, hut the 
eostm appear to he much simpler than in the left — there is a less marked 
sej)aration into primary, secondary, and tertiary. In one specimen the })rimary 
costae show traces of bifurcation, hut not so the others. IMcCoy’s figure docs 
not represent a full grown individual; we jiossess much larger exam^ilcs. 
Localiiies and Horizon. — Portion 52, Parish Hawkins, County Phillip 
( C. E. 3Inrton) ; Creek, one and a half mile south-Avest of Dapto ( C. Cullen) ; 
near Cessnock ((7. Cullen)-, Black Head, Gerringong {IE. S. Eun, B. G. 
Engelhardt) ; Albion Park Hoad, Jamheroo {B. G. Engelhardt) ; AAMllongong 
{C. Cullen)-, Ravensheld [T. IF. E. David)-, Bundanoon ((7. Cullen)-, 
Parley (,/. IFaierhoufte)-, Cevriw^ow^ {R. Etheridge, JF. S. Dun)-, llutlierford’s 
Quarry, AV. Maitland; Locliinvar; Portion 110, Parish. AA^ingen, County 
Brisbane [C. Cullen)-, half a mile south-east of Bed Bock, Drake [C. S. 
IFilJdnson) . — Permo-Carboniferous — ^Lower and Upper Marine Series. 
Collections. — Mining and Geological Museum, and Australian Museum. 
Deltopectex leniusculijs, Dana. 
(Plate m, Fig. 1; PI. IV; PI. VI, Fig. 1; PI. VII, Figs. 1 aii<l 2; PI. X, Figs. 1 and 2i 
PI. XT, Fig. .3.) 
Pccten Icniusculus, Dana, Am. Jourii. Sci., 1817, IV, p. 160. 
,, Dana, Wilkes U. S. Exjilor. E.xped., 1849, X ((leol.), p. 704, Atlas, t. 9, 
f. 6 a and b. 
Observations . — Dana tigured lioth the convex and flat valves, AAuth 
rectangular auricles, hut the latter do not appear to be ])crfect. 
There is only one other figure of this species extant, so far as avo 
knoAV : — 
1. Aviculopecten Icniusculus, ,De Koiiinek,^ a coiwex vahm devoid of 
the auricles. 
* De Koninck — Recli. Foss, Pal. Nouv.-Galles clu Sad, Pt. 3, 1877, p. 151, t. 21, f. 3, 
