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 foui' 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 I am 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 XLii, Figs. 1-5. 



Ammonites Vanuxemi Morton : Am. Jour. Sci., 1st ser., vol. 18, PI. in, Pigs. 3, 4 ; 



Synopsis, p. 38, PL ii, Figs. 3, 4. 

 A. Delawarensis (young specimen) Gabb : Synopsis, p. 18. 

 Not A. Vanuxemi Lea : Trans. Am. Phil. Soc, 2d. ser., vol. 7, p. 354, PL viii, 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 



