CEPHALOPODA OF THE CRETACEOUS MARLS. 253 
The septa are marked by three lobes and an imperfect fourth one on 
the inner margin, and by three sinuses. The dorsal lobe has a pair of 
short, principal, digitate branches, with several small digitations along its 
sides. First lateral lobe moderately large, with four principal, much ser- 
rated branches, and two or more minor ones on the neck. The second 
lateral is irregularly branched, having two or three divisions, and the one 
bordering the umbilicus has the margin simply undulated. The first sinus 
is very large and divided in the middle by a long, slender, digitate, minor 
lobe, which extends nearly or quite half the length of the dorsal lobe. The 
second sinus is not more than two-thirds the size of the first, and far less 
distinctly divided. The small umbilical sinus has the margin rather deeply 
undulated only. The margins of the sinuses are clavately undulated, and 
those of the lobes more sharply serrated; the number and complication of 
these features varying of course with the size and age of the shell. In 
the young specimens, which have the characters of A. Vanuxemi Morton, 
the complications of the lobes and sinuses are more simple, although all the 
features are present, as may be seen by the diagrams given on the plate. 
In Dr. Morton’s figure in his synopsis the septa are very incorrectly 
represented, while the nodes and ridges are very strongly shown. 
Formation and locality: The type specimens are all from Delaware, so 
far as Lam aware. Dr. Morton gives the Delaware and Chesapeake Canal, 
and states that he had another from Alabama. I have not seen it from else- 
where than Delaware and New Jersey. The small specimen figured on our 
plate is from near Burlington, New Jersey, and is in the Am. Mus. of Nat. 
Hist. 
AMMONITES VANUXEMI. 
Plate xu, Figs. 1-5. 
Ammonites Vanuxemi Morton: Am. Jour. Sci., Ist ser., vol. 18, Pl. m1, Figs. 3, 4 ; 
Synopsis, p. 38, Pl. u, Figs. 3, 4. 
A. Delawarensis (young specimen) Gabb: Synopsis, p. 18. 
Not A. Vanuxemi Lea: Trans. Am. Phil. Soe., 2d ser., vol. 7, p. 254, Pl. vin, Fig. 5. 
This species appears to have been described from specimens of small 
size, and imperfect. Dr. Morton remarks under the description given in his 
Synopsis, p. 38, that the ‘supposed diameter” is 3 inches; also, that “larger 
