388 Systematic Paleontology 



Family ENGONOCERATIDAE 



Genus SPHENODISCUS Meek 

 [4th Ann. Rept. TJ. S. Geol. and Geog. Survey, Terr., 1871, p. 298] 

 Type. — Ammonites lenticularis Owen. 



" Shell with periphery cuneate ; umbilicus very small ; volutions each 

 almost entirely embraced by the succeeding one ; septa with the first five 

 or six lateral sinuses provided with only a few short, nearly simple, obtuse 

 divisions; while the others are simple, and usually broadly reniform at 

 the ends."— Meek, 1876. 1 , 



Sphenodiscus lobatus (Tuomey) Meek 

 Plate XIII, Fig. 10 



Ammonites lobata Tuomey, 1854, Proc. Acad. Nat. Sci., Phila., vol. vii, p. 



168. 

 Ammonites lobatus Meek, 1864, Check List Inv. Fossils, N. A., Cret. and 



Jur., p. 24. 

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

 Sphenodiscus lobatus, Meek, 1876, Rept. Inv. Cret. and Terr. Fossils, Up. 



Missouri, p. 463. 

 Ammonites (Sphenodiscus) lenticularis Whitfield, 1892, Mon. U. S. Geol. 



Survey, vol. xviii, p. 258, pi. xli, figs. 8, 9. 

 Sphenodiscus lobatus Hyatt, 1903, Mon. U. S. Geol. Survey, vol. xliv, p. 66, 



pi. vi, figs. 1, 2; pi. vii, figs. 1, 2; pi. ix, figs. 11-13. 

 Sphenodiscus lobatus Weller, 1907, Geol. Survey of New Jersey, Pal., vol. 



iv, p. 828, pi. cvi, figs. 1, 2. 



Description. — " Shell discoid, smooth, thin towards the circumference ; 

 dorsal lobe finely serrate ; lateral lobes terminating in large bilobed cells. 

 .... This fossil, of which I have only a fragment, resembles A. placenta 

 but is distinguished from it by the remarkable cells that terminate the 

 lateral lobe." — Tuomey, 1854. 



" A fine specimen .... from Bipley group, Lander's Mill, Tippah 



County, Mississippi, is 111 mm. in diameter There are obscure 



fold-like costse indicated outside of the greatest transverse diameter, 

 which is nearly central ; internally the surface is slightly concave. There 

 are no umbilical shoulders and no flat umbilical zone and umbilical open- 

 Etymology: <r<t>riv, wedge; sisnos, disc. 

 1 Rept. U. S. Geol. Survey, Terr., vol. ix, p. 463. 



