280 PALEOZOIC PALEONTOLOGY. 
are usually inconspicuous or obsolete, but towards the anterior mar- 
gin, in old shells, they become coarse and crowded. 
The dimensions of an average-sized pedicle valve are: length, 27 
mm.; width, 24 mm.; convexity, 14 mm. The dimensions of the 
largest pedicle valve observed are: length, 44 mm.; width, 31 mm.; 
convexity, 23 mm. 
Remarks.—This shell, in its typical American form, is exceedingly 
abundant in the lower beds of the Coeymans lmestone, and, except 
in characters due to different. stages of growth, does not exhibit 
any great variation. Formerly the species was placed in the genus 
Pentamerus, and, because of its great abundance, the formation was 
designated the ‘“‘Pentamerus limestone” in the older geological and 
paleontological reports of New York State. The species may always 
be recognized by its subglobular form and its smooth umbonal region. 
Frequently, in breaking the rock containing specimens of this shell, 
individuals are spht longitudinally along the line of the median 
septum, and in such specimens the characteristic median septum can 
be clearly seen. 
GYPIDULA GALEATA (Dal.) var. 
Plate XXVIII., Figs. 9-12. 
In the upper portion of the Coeymans limestone near Hainesville 
there occurs a form of Gypidula which may, perhaps, be considered 
as a variety of G. galeata. It differs from the typical American form 
of the species in having somewhat finer and more conspicuous radiating 
plications and in having the fold and sinus entirely obsolete. 
GYPIDULA ANGULATA N. sp. 
Plate XXVIII., Figs. 13-21. 
Description.—Shell subglobular in form, usually wider than long. 
Pedicle valve suboyate or subquadrate in outline, gibbous; the beak 
prominent and strongly incurved, the median portion of the shell ele- 
vated in a sharply-defined fold, which reaches to the umbonal portion 
of the valve. The fold is sometimes plane on top, but usually bears 
three prominent, subangular plications which reach to the umbo. The 
