378 Systematic Paleontology 



The single fragment collected in Maryland differs from Morton's type 

 in the higher lateral compression and the much less prominent nodes. 

 The sutural characters are similar and, for that reason, they have been 

 united until stronger evidence comes to light for their separation. 



Occurrence. — Matawan Formation. Post 218, Chesapeake and Dela 

 ware Canal, Delaware. 



Collections. — Maryland Geological Survey, Philadelphia Academy of 

 Natural Sciences. 



Outside Distribution. — Magothy Formation. Cliffwood clay, New 

 Jersey. Monmouth Formation. Navesink marl, New Jersey. Eutaw 

 Formation (Tombigbee sand member). Exogyra ponderosa zone, Mor- 

 toniceras subzone, Columbus, Mississippi; Warrior, Tombigbee and Ala- 

 bama rivers, Alabama, f Fox Hills. Mouth of Judith River, Montana. 



Family DESMOCERATIDAE 



Genus PACHYDISCUS Zittel 

 [Handb. Pal., Ab. I, Bd. II, 1885, p. 466] 



Type. — Pachy discus wittehindi (Schliiter). 



Large ventrieose, heavy-shelled Ammonoids, venter rounded; external 

 surface corrugated with heavy, occasionally nodose ribs, either simple or 

 bifurcating, most vigorous in young forms; sutures complex and finely 

 serrate. 



The genus is widespread and abundant in the Cretaceous faunas, but is 

 restricted, apparently, to that epoch. 



Pachydiscus complexus (Hall and Meek) Weller 



Ammonites complexus Hall and Meek, 1855, Mem. Am. Acad. Arts and Sci., 



n. s., vol. v, p. 394, pi. iv, figs, la-lf. 

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



Jur., p. 24. 

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

 Ammonites complexus Meek, 1876, Rep. Inv. Cret. and Ter. Fossils, Up. 



Missouri, p. 447, pi. xxiv, figs, la-lc. 

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



p. 249, pi. xli, figs. 5-7. 

 Pachydiscus complexus Weller, 1907, Geol. Survey of New Jersey, Pal., vol. 



iv, p. 819, pi. ci, figs. 3, 4. 



Etymology: vax^s, thick ; 5iVKos,disc. 



