Maryland Geological Suetbt 391 



straighter and differently tuberculated costae, and differences in the forms 

 and proportions of its septa, lobes and sinus." — Meek, 1S?(>. 



MORTONICEBAS DBLAWAJIENSIS (Morton ) 



Plate XII, Fig. 5 



Ammonites delawarensis Morton, 1830, Am. Jour. Sci., 1st ser., vol. xviii, 



pi. ii, fig. 4. 

 Ammonites vanuxem.i Morton, 1S30, Ibidem, pi. iii, figs. 3, 4. 

 Ammonites delaioarensis Morton, 1834, Syn. Org. Rem. Cret. Group, U. S„ 



p. 37, pi. il, fig. 5. 

 Ammonites vanuxemi Morton, 1834, Ibidem, p. 38, pi. ii, figs. 3, 4. 

 Ammonites delawarensis Meek, 1S64, Check List Inv. Fossils, N. A., Cret. 



and Jur., p. 24. 

 Ammonites delaioarensis Conrad, 1868, Cook's Geol. of New Jersey, p. 730. 

 Ammonites delaicarensis Whitfield, 1892, Mon. U. S. Geol. Survey, vol. xviii, 



p. 252, pi. xlii, figs. 6-9; pi. xliii, figs. 1, 2. 

 Ammonites vanuxemi Whitfield, 1892, Mon. U. S. Geol. Survey, vol. xviii, 



p. 253, pi. xlii, figs. 1-5. 

 Ammonites delawarensis Roberts, 1895, Johns Hopkins Univ. Circ, vol. xv, 



No. 121, p. 16. 

 Ammonites delawarensis Johnson, 1905, Proc. Acad. Nat. Sci., Phila., p. 27. 

 Ammonites vanuxemi Johnson, 1905, Ibidem. ., 



Mortoniceras delawarensis Weller, 1907, Geol. Survey of New Jersey, Pal., 



vol. iv, p. 837, pi. ciii, fig. 1; pi. civ, figs. 1-5. 



Description. — " Volutions uncertain ; each whorl furnished with ele- 

 vated transverse ridges, which bifurcate about half-way across and ter- 

 minate 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 in.'" — Morton, 1834. 



" 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 .4. 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 dorsum 

 being triply keeled ; the marginal keels being formed of obliquely elon- 

 gated nodes formed by the extremities of the numerous, rounded eostas 

 which cross the sides of the volution. A row of nodes marks the ends of 

 the costas along the margin of the umbilicus, and three other lines occur 



