CEPHALOPODA— AMMONOIDEA. 



153 



242. P. arnoldi Hyatt and Smith. (Fig. 1402, ^-7.) Triassic. 



Whorls subquadratic in section, shghtly higher than wide, slowly 

 increasing in size, scarcely indented by inner whorl ; suture shows 

 second lateral lobe just above umbilical shoulder, as well as internal 

 lateral. 



Meekoceras beds (Lower Triassic) of Aspen ridge, Idaho. 



Pinipf" 



Fig. 1402. a-c, Sageceras gabbi, X /^j ^"d suture enlarged ; d-f, Pseudosage- 

 ceras in ermontanum, X ^» and suture ; g-j, Paralecanites arnoldi^ X Yzi ^'^^ suture 

 enlarged; showing divided ventral, tw^o lateral and one internal lobe. (After Hyatt 

 and Smith. ) 



CII. Meekoceras Hyatt. 



Compressed, discoidal, involute or evolute, with flattened sides; 

 narrow venter, flattened or rounded but without keel or furrow ; sur- 

 face smooth or with fold-like ribs ; sutures ceratitic, with rounded 

 entire saddles, and serrated lobes ; external lobe short and divided 

 by siphonal saddle ; the two lateral lobes are longer and there is an 

 auxiliary series in most species, consisting of a single ceratitic or 

 goniatitic lobe, or a series of denticulations ; antisiphonal lobe 

 divided, flanked by a single lateral. Triassic. 



243. M. gracilistriatum (White). (Fig. 1403, o-c.) Triassic. 



Deeply embracing; outer whorl concealing one fourth of inner; 

 umbilical shoulder abruptly rounded; venter broad and flat, with 

 sharp lateral angles; surface with low folds. (Type of genus.) 



Lower Triassic (Meekoceras beds) of Idaho and California. 



