274 PALEONTOLOGY OF NEW JERSEY. 
third of its length, but is again abruptly expanded just behind the aperture; 
the opening itself having been circular and smaller than the tube behind it. 
Surface of the cast finely and closely annulated, the annulations having a 
direction just perceptibly backward in crossing from the inner to the con- 
vex surface, and count just eight annulations in the space of one-fourth of 
an inch on the largest part of the outer tube; on the inner concave face the 
annulations are somewhat finer, as many of them are doubled at the edge 
of the concavity, giving in the aggregate nearly one-third more annulations 
within a given distance. On the back of the cast two lines of minute nodes, 
marking the crests of the annulations for a short distance behind the aper- 
ture, are faintly perceptible under a good magnifier. 
On the posterior extremity of the outer chamber the lobation of the 
last septum is obscurely marked, showing a moderately strong dorsal lobe, 
with a larger lateral lobe on each side, while a large bilateral sinus has 
occupied each edge with a lobe on each ventral side, and a very small ven- 
tral lobe on the inner surface. The details of the lobes and sinuosities are, 
however, too badly defined to be traced. The surface of the shell of the 
septum is beautifully iridescent, and slight traces of iridescence are percepti- 
ble on other parts of the cast. 
The specimen here used and figured is Morton’s type of the species, 
and is also that used by Mr. Conrad for the type.of his genus Solenoceras. 
As yet no other has been observed so far as I can ascertain. It differs 
from the species described as Ptychoceras Mortont by F. B. Meek in his 
Vert. Paleont. U. 8. Geol. Survey of the Terr. p. 412, Pl. xx, Fig. 4, in 
the direction of the transverse ridges which are more direct, and possibly 
in their beng somewhat finer and more regular; on the whole, however, 
it is very similar. From P. Meekanum Whitf., of the Black Hills report, it 
differs much more widely in that that species is more coarsely annulated, 
and the annulation much more acute and oblique. 
Formation and locality: The type specimen, as stated under the original 
description by Dr. Morton, is from the Lower Green Marls, at the Deep 
Cut of the Chesapeake and Delaware Canal, Delaware. It is very 
probable, however, that by careful observation it might be discovered in 
the Lower Marls in New Jersey. The specimen is in the collection Acad. 
Nat. Sci., Phila. 
