GASTEROPODA. 
127 
PORCELLIA NAIS. 
PLATE XVI. FIGS. 27, 28 ; AND PLATE XXVI, FIGS. 26-28. 
Gyroceras Nais, Hall. Descriptions of New Species of Fossils, etc., p. 40. 1861. 
“ “ “ Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 68. 1862. 
Porcellia “ “ lb., Explanations pi. 6, fig’s. 5 and 6. 
.Porcellia “ “ Illustrations of Devonian Fossils : Gasteropoda, pi. 16. 1876. 
Shell consisting of about four volutions, which are somewhat rapidly expanded 
from the apex towards the aperture; volutions subangular and nodose on 
the sides, and rounded on the back; the dorsum a little elevated on each 
side of the mesial band; the ventral side sloping abruptly into the umbil¬ 
ical depression. The aperture has probably been somewhat broadly sub- 
reniform. 
Surface of the umbilical slopes of the volution marked by strong, rounded, 
transverse striae, which are sometimes bifurcated toward the side of the 
shell, and are crossed by revolving lines, giving it an undulated or sub¬ 
nodose aspect. The back of the shell, in a partial cast, is conspicuously 
marked by flattened revolving bands, which are crossed by less strong 
transverse striae. The dorsum is marked by a narrow depressed band, on 
which the striae make an abrupt retral bend, indicating the sinuosity in 
the margin of the aperture. About half-way from the dorsal line to the 
angular side of the volution, commence low elevations which become strong- 
oblique ridges or elongate nodes, limited by the angular margin, and not 
passing to the ventral region nor marking the umbilical slope of the 
volutions. 
The larger specimen, which is figured on plate 16, preserves about one 
volution and a half; it is imperfect towards the aperture, and the inner volu¬ 
tions are broken away. It has a diameter of about two inches. 
A fragment, consisting of nearly three of the inner volutions, while preserv¬ 
ing the general features already noticed, shows the dorsal side and umbilical 
slopes of the volutions to be cancellated by distinct elevated equal strife, which 
are conspicuously nodulose at their crossing; it also shows that the entire shell 
consists of at least four volutions. 
