~~ 
Oo 
Ww 
PALEOZOIC PALEONTOLOGY. 
The specimens observed are all more or less fragmentary and imper- 
fect, and the description given above has been drawn up largely from 
New York specimens. The species is especially characterized by the 
large size which it attains. 
MOLLUSCA. 
PELECYPODA. 
ACTINOPTERIA TEXTILIS (Hall). 
Plate XLIIIL., Figs. 138-14. 
1859. Avicula textilis Hall, Pal. N. Y., vol. III., p. 288, pl. 52, figs. 
9-10, pl. 53, figs. 2, 3, 5, 7, 10. 
Description.—Body of shell obliquely subovate, anterior wing 
small, convex; posterior wing large, produced along the hinge-line, 
flat posteriorly, becoming convex towards the beak. Hinge-line longer 
than the vertical height of the shell, the beak situated near its an- 
terior extremity. Surface of left valve marked by strong, sharply- 
elevated, more or less alternating radiating ribs, much narrower than 
the intervening depressions, and by fainter concentric lines, which 
usually form slight nodes where they cross the radiating ribs, the 
nodose appearance being more conspicuous towards the beak. Upon 
the wings the radiating ribs become much reduced, being about equal 
in size with the concentric markings. The right valve is more nearly 
flat than the left, and is nearly smooth, or with a few faint, radiating 
ribs upon the central portion of the shell. 
The dimensions of a rather large individual are: vertical height, 
7 mm.; oblique height from beak to the postero-basal extremity, 
32 mm.; length of hinge-line, 29 mm. 
vemarks.—This species identified as A. textilis is a common one 
in the fauna of the “trilobite bed.” The specimens observed vary 
in size from no more than 6 mm. or 8 mm., to the maximum height 
of over 30 mm. The angle of obliquity also varies from 60° or less 
to nearly 80.° The shell has the general aspect of both A. tevtilis 
and A. communis of the Helderbergian faunas, but does not agree 
exactly with the descriptions of either of these species. It seems to 
be closest to A. textilis, and is therefore so identified. 
9 
~ 
‘ 
