252 PALEONTOLOGY OF NEW JERSEY. 
AMMONITES DELAWARENSIS. 
Plate xxi, Fig. 6-9; and Plate xxi, Figs. 1, 2. 
Ammonites Delawarensis Morton: Am. Jour. of Science, Ist ser., vol. 18, Pl. 11, 
Fig. 4; Synopsis, p. 37, Pl. 2, Fig. 5; Gabb, Synopsis, p. 9; Meek, Check 
List Cret., p. 24; Geol. Surv. N. J., 1868, p. 730. 
Dr. Morton describes this species as follows: ‘‘Volutions uncertain; 
each whorl furnished with elevated transverse ridges, which bifurcate about 
half way across, and terminate in prominent tubercles on the margin; 
ridges marked by three or four conspicuous nodes; back between the 
tubercles convex; probable diameter from 8 to 12 inches.” 
The shell seems to have been a very variable one, especially so when 
different periods of growth are considered. The young form was described 
by Dr. Morton as A. Vanuxemi, in which condition it is somewhat discoid, 
with a moderately large umbilicus with vertical sides; about one-half only 
of the volution being embraced by the succeeding one; the narrow dor- 
sum being triply keeled; the marginal keels being formed of obliquely 
elongated nodes formed by the extremities of the numerous, rounded costz 
which cross the sides of the volution. A row of nodes marks the ends of 
the costee along the margin of the umbilicus, and three other lines occur 
at nearly equal distances apart, between the first and the marginal row, 
which forms the lateral keel. When more advanced in growth the sides 
become rounded and convex; the dorsum proportionally wider and less 
distinctly keeled; the volutions somewhat more involved within the outer 
one, which gives a correspondingly narrower umbilicus in proportion to the 
entire diameter; the ridges crossing the sides are proportionally less ele- 
vated and the nodes less conspicuous. In a large cast sent me, as one of 
the type specimens, from the Acad. Nat. Sciences, Philadelphia, the thick- 
ness at the edge of the umbilicus is 23 inches, when the width of the volu- 
tion is 34 inches. A small specimen (figured on Pl. xu, Fig. 6), apparently 
entirely uncompressed, presents a width on the side of the volution of three- 
eighths of an inch, and a diameter of one-sixteenth less at the edge of the 
umbilicus. The same features of the surface are present on both speci- 
mens, differing only in degree. 
a 
