ORDOVICIAN FAUNAS. 147 
ORBICULOIDEA LAMELLOSA (Hall). 
Plate IX., Figs. 1-2. 
1892. Orbiculoidea lamellosa Hall and Clarke, Pal. N. Y., vol. VIIL., 
pt. I., pl. 4 #, fig. 12. 
Description.—Shell depressed-conical, nearly circular in outline, 
the apex of the brachial valve situated about one-third of the breadth 
of the shell from the margin. Surface marked by rather irregular, 
elevated, more or less lamellose, concentric lines, the grooves between 
the lines being rather wider than the ridges themselves. 
Pedicle valve not observed in the New Jersey collections. 
The dimensions of a nearly perfect brachial valve are: length, 9.5 ~ 
mm.; width, 8.75 mm.; convexity, 2.5 mm. 
Remarks.—With the possible exception of a single one, all the 
specimens of Orbiculoidea which have been observed in the Trenton 
limestone fauna of New Jersey belong to this species. It is char- 
acterized by rather conspicuous, sublamellose, concentric markings, 
and seems to agree with the descriptions and illustrations of O. 
lamellosa. 
ORBICULOIDEA sp. undet. 
Plate IX., Figs. 5-6. 
A single specimen of a peculiar shell, which is apparently one of 
the inarticulate brachiopods, has been observed in a collection of 
Trenton limestone fossils from near Branchville, New Jersey. The 
form of the shell is obliquely subconical, the elevation of the bluntly- 
rounded apex being about three-fourths the width of the shell. The 
length is somewhat greater than the width, the outline of the margin 
being nearly elliptical. 
The dimensions of the specimen are: length, 13 mm.; width, 10 
mm.; convexity, 7.5 mm. 
In general form the shell resembles some of the simple, cap-shaped 
gastropod shells, but the shell substance is that of the inarticulate 
brachiopods, such as Orbiculoidea, in which genus the shell has been 
placed provisionally. The pedicle valve has not been observed. 
