80 
PALAEONTOLOGY OF NEW YORK. 
Genus (or Subgenus) PENTAGONIA, Cozzens. 1846. 
PLATE XLII. 
1841. Atrypa, Conrad. Fifth Ann. Kept. Geol. Survey of N. Y., p. 56. 
1846. Pentagonia, Cozzens. Annals of the Lyceum of Nat. Hist, of N. Y., vol. iv, p. 158, pi. x.fig-. 3. 
1857. RTiynchonella, Hall. Tenth Kept. N. Y. State Cab. Nat. Hist., p. 125. 
1860. Athyris f, Billings. Canadian Journal, vol. v, p. 279, figs. 39-42. 
1861. Gonioccelia, Hall. Fourteenth Kept. N. Y. State Cab. Nat. Hist., p. 101. 
1862. Mo-istella, Hall. Fifteenth Kept. N. Y. State Cab. Nat. Hist., pi. ii, figs. 17-25 ; pi. xi, fig. 10. 
1863. Athyns, Billings. Geology of Canada, p. 373, fig. 396. 
1864. Pentagonia, Meek and Havden. Paleontology of the Upper Missouri, p. 16. 
1867. Meristella {Pentagonia), Hall. Paleontology of N. Y., vol. iv, pp. 309-311, pi. 1, figs. 18-35. 
1889. Menstella, Nettblroth. Kentucky Fossil Shells, p. 99, pi. xv, figs. 9-16. 
Among the species of meristelloid structure, an interesting variation in the 
form of the shell is presented by the little M. lenta, Hall, of the Oriskany sand¬ 
stone. Here the pedicle-valve is very shallow and so deeply sinuate as often 
to appear concave; the brachial valve is quite convex, especially along the 
median line. A more extreme development of this form is seen in the Atrypa 
unisulcata, Conrad, of the Corniferous limestone and the Hamilton group, and 
it was to this species that the name Pentagonia was early applied by Isaachar 
Cozzens.* The description of the genus was brief, but the accompanying 
figures clear and unmistakable. This species is characterized by a very broad 
sinus on the pedicle-valve, which is limited by divergent carinse, outside of 
which the cardinal or lateral slopes are very abrupt. On the brachial valve is 
a rounded median fold, which may be divided on its summit by a narrow sinus 
and in the umbo-lateral region are two short folds or flanges, beginning at the 
hinge-line, having a slightly sinuous curve and terminating before traversing 
much more than one-third the length of the valve; occasionally there is a 
second of these ridges on each side. 
The muscular impressions of the valves are essentially as in Meristella. 
The hinge-plate has a peculiar structure ; it arises vertically from the bottom 
of the valve, presenting an erect, concave anterior face, which is traversed by 
a faint median ridge continuous with the septum of the valve. The posterior 
* Defscription of Three New Fossils from the Falls of the Ohio ; Annals of the New York Lyceum of 
Natural History, vol. iv (1846), p. 158, pi. x, figs. 3 re, 5 (Pentagonia Peersi = Atrypa unisulcata, Conrad). 
