40 CARBONIFEROUS AMMONOIDS OF AMERICA. 



its height. The surface of the cast is ornamented with sigmoidal ribs, whicli 

 bend backward toward the venter. These ribs are fine and sinuous, showing- 

 with unusual distinctness on the cast. The outer shell is unknown, but 

 they should be even more distinct on it. 



Septa ceratitic, lanceolate. The ventral lobe seems to be undivided, 

 the first lateral is indistinctly tripartite, the second lateral distinctly serrated, 

 and the third is bifid; these are followed by a series of six unserrated 

 auxiliary lobes, growing smaller and shorter toward the umbilicus. 



From its small size, its shape, and the primitiveness of its septa, this 

 specimen might be considered as the young of Prodromites gorhyi, but in all 

 known specimens of that species the surface of the cast is perfectly smooth. 

 It undoubtedly belongs to that genus, and is perhaps the young of some 

 unknown form, but probably not that of I'rodromites gorhyi, nor of P. 

 prcematurus ; a name is therefore given to it by which the mature form may 

 be known when it is discovered. 



Only a single specimen is known, No. 7682, paleontologic collection, 

 Walker Museum, University of Chicago. The wi-iter's thanks are due Dr. 

 Stuart Weller for the use of the type. Diameter of the type, 28 mm. 



Occurrence. — Lower Carboniferoiis, Kinderhook stage, Chouteau lime- 

 stone, Pettis County, j\Io. 



Prodromites pr^maturus Smith and Weller. 



PI. XXV, figs. 3 and 4. 



1901. Prodromites prsematurus, Smith and Weller, Jour. Geol., Vol. IX, No. 3, 

 p. 261, PI. VIII, figs. 3 and 4. 



Type of species is specimen No. 6223, paleontologic collection, 

 Walker Museum, University of Chicago (Gurley collection). Form later- 

 ally compressed, discoidal, involute, deeply embracing, with naiTow umbil- 

 icus, narrow, slightl)^ flattened abdomen surmounted by a hollow keel 

 3 mm. high. Whorl indented by the preceding whorl to a little over one- 

 third of its height. Surface smooth, so far as known. 



The septa are complex, ceratitic, with rounded, entire saddles, serrated 

 lateral lobes, and a series of auxiliaries above the umbilicus. The ventral 

 lobe is narrow and undivided; the first lateral is longer and three-pointed; 

 the second lateral, four-pointed; the third lateral, bifid; the fonrth lateral, 

 bifid; then begins a series of auxiliary lobes, undivided and pointed, seven 

 in number. 



