56 CARBONIFEROUS AMMONOIDS OF AMERICA. 



Shell evolute, discoidal, little embracing-; cross section elliptical; 

 impression moderate. Whorls at least four in number, with slow increase 

 of growth. Umbilicus wide. Surface smooth. Length of body chamber 

 unknown. 



Septa lanceolate and close together. Ventral lobe long, pointed, and 

 narrow; first and second lateral lobes not so large as the ventral and not 

 sharply terminated. Auxiliary lobe outside of the umbilical border short 

 and blunt. Antisiphonal lobe deep. 



The nearest American species is P. lyoni Meek and Worthen, from 

 which P. marsJiallensis differs in the additional pair of lobes outside of the 

 umbilical border and in the greater length of the ventral lobe. It is also 

 somewhat more involute than P. lyoni. Winchell thought this species to 

 be nearest akin to P. mtxolohus Phillips, which was chosen by Mojsisovics 

 as the type of Frolccanites, but the lobes of P. mixolohus are not mucronate 

 but rather club-shaped, and the auxiliary lobe is nearly as large as the 

 principal laterals, and the ventral lobe seems to be very small. 



Occurrence. — P. marshallensis was found in the Lower Carboniferous 

 Kinderhook stage, Marshall group, at Marshall, Moscow, Battle Creek, 

 Napoleon Cut, Mich., and in the Waverly group at Weymouth and Newark, 

 Ohio. 



Snperlamily aLYFHIOCER^TID^E. 



This group was established by Hyatt" to include a number of species 

 from the Upper Devonian, Carboniferous, and Permian. The oldest 

 genera are Agankles (Brancoceras) and Prionoceras, which began in the 

 Upper Devonian and attained their acme in the Lowei- Carboniferous. 

 Both genera are smooth-shelled, and })oth liave a pointed, undivided, 

 ventral lobe and two pairs of lateral lobes, of which the first is angular ; 

 the saddles of most species of both genera are broadly rounded, although 

 on Prionoceras (jToniatites) helvalianum de Koninck the first lateral saddles 

 are angular. The only difference between tlie two genera is that Aganides 

 is compressed, high-whorled, almost discoidal, and very invohite ; while 

 Prionoceras is broad, low-whorled, and evolute. Hyatt considered Bran- 

 coceras as the radicle of the Glyphioceratidse, and traced the group from 

 Anarcestes of the Lower Devonian, through Tornoceras {Parodoceras) of the 



«Proc. Boston Soc. Nat. Hist., Vol. XXII, \>. 322. 



