171 
In adult specimens tlie ventral furrow, midway in its course, rises abruptly 
towards the front. The dorsal valve is rather regularly ventricose, and its 
dorsal ridge not often strongly developed ; there is always one more plication 
in the dorsal ridge than there is in the ventral furrow. 
Dimensions. — The largest of the Australian specimens was eighteen 
millimetres broad by twelve long, and its thickness seven millimetres. 
Delations a, net Differences. — This species is easily distinguished from 
its Carboniferous allies by its general shape, and by the form of its plications. 
I have before stated that the Dhtjnchonella figured by me under the name 
D. Davreuxkma does not form a variety of this species, as Mr. Davidson 
supposed, but is a perfectly distinct species. 
Horizon and Localities. — This species seems to have existed through- 
out the Carboniferous Period properly so called, beginning in the Tournai 
beds, where it is found abundantly. It is even more abundant in the upper 
strata of Anseremme and Vise. It is equally abundant about Glasgow ; is 
found in the Valley of Sichon, Prance, and at Bleiberg, in Carinthia ; it is 
not uncommon in England and Ireland, and it has been found in Pussia and 
Thibet. In New South Wales it was discovered at Coyeo, on the Page 
River, between the Karua River and Dungog, and at Burragood in a yellowish 
sandstone, and in a brownish argillaceous limestone. 
PvnTNCHONELLA INVEESA, L. G. dc Koninch} 
PL XI, Eg. 11. 
This shell is one-third longer than broad, subpentagonal, and having 
its greatest transverse diameter in about the middle of its length. The 
ventral valve is regularly curved, and is furnished with a mesial fold extend- 
ing from the beak to the base, becoming thicker in its course; two other 
folds, thicker and oblique, are placed on each side of the mesial fold. The 
furrows separating these folds are rounded at the bottom. The beak is 
rather thick, only slightly incurved, obliquely truncated, with an oval, rela- 
tively large, foramen. The dorsal valve is nearly as deep as the ventral valve, 
and has a rather deep, but not very broad, mesial furrow, limited on each side 
’ [This has been shown by Mi’. R. Etheridge, Junr. , to be a species of Dielasma. Records Geol. Survey 
N. S. Wales, 1898, V, Pt. 4, p. 175, t. 19, f. 1-13.— W.S.D.] 
2 A 
