Report of the State Geologist. 



and fasciculation, their outcome being a totally distinct expression in the 

 exterior aspect of the shell. Septation is nepionic with reference to the 

 standard. 



Manticoceras nodifer. 



So far as this species is understood, it indicates rapid acceleration in the 

 character of its ornament, the nodes on the early whorls being an extremely 

 advanced outcome of the regular concentric striation. In other respects, 

 umbilication, whorl section and septation, the species is much more ele- 

 mentary in its expression. 



Manticoceras Pattersoni, var. styliophilum. 



We find here acceleration well marked in the narrow, depressed convex 

 whorl section, and some slight degree of this quality in the increased umbili- 

 cation, but in other respects this shell does not depart from the 

 standard form. 



Manticoceras sororium. 



Tachygenic in its early acquisition of a narrow sagittate whorl section. 

 Like Mantic. rhynchostoma it is restricted to the western part of the Intu- 

 mescens province where Mantic. Pattersoni is not yet known to occur. 



Manticoceras accelerans. 



Distinct evidence of acceleration in a stage at, or approaching, epheby is 

 shown in the close crowding of the septa. In other respects present evidence 

 is not conclusive. 



Manticoceras oxy. 



The extreme lateral compression and carination of the whorl indicates 

 great acceleration in this character, a fact distinctly fortified by the develop- 

 ment of low pilae on the final whorl, the ultimate condition of the sutures, 

 and the great size of the shell. This species affords the most pronounced 

 example of acceleration. 



Manticoceras vagans. 



This species conforms to the standard, so far as known, except in the 

 extreme acceleration of the whorl section which is acute and carinate in early 

 ephebic, if not, indeed, at late neanic stages. 



The following diagram is designed to express the variations of these 

 various paraphases of Manticoceras, as expressed above. Mantic Patter- 

 sorii, as the standard of reference, is represented by a straight horizontal line. 



