AN \',l V. - 3. 71 



III. 



GENESIS OF « BABAt TERISTK - 

 A\\ ob thf. Gbnxsis of Pbogbbssivb Chabactbrie 



TIIK introduction of the peculiar pita and single channelled abdomen in 

 Schlotheimia, which occurred in the earlier Bpecies, must l>r regarded 

 complication, since it is not onlj a new characteristic, but it is 

 correlative with - in the amount of involution, and with the 



advent - having inure compressed, more involute and Bub-acute whorls. 



The waBhneroceran series introduces the observer to Schlotheimia by it- inter- 

 mediat modifications when one begins with tin- radical stork. Psiloo i 



Undoubtedly the Bteady increase of involution in successive Bpecies of the 



and Bchlotheimian Beries is. like the similar phenomena 



_ urded as progressive. This is clearly Bhown, both by 



■ ■ in individuals throughout each Beries, and also by 



tin- tact that these changes are in accord with the general progression of the 



whole group. 



The yo - we have remarked above, were closer coiled during 



lie than in the Paleozoic, and the adult forms were more involute as 

 a rule in th<- Trias and Jura, than in the earlier geologic periods, The genesis 

 of this pro haracter independently in each series may I"- seen bj ex- 



amining the different series in the four summary plates, and we need not allude 



hnpter. It is also interesting to note, that the most 



parallelisms in this respect are to !><• found between thi which are 



widelj I. Thus the extreme aberrant forms of the family, namely, 



ras, the radical Psiloceras, and the opposite extremes 



of the nd Oxyno *ed highly involute 



com pre i whorls. 



Lheroftbe first three bad any species with quadragonal whorls; the sheila 

 of the helmet-shaped or secondary radical form. Th< 

 nn ip| mi t.. the subquadragonnl in the most discoidal Bpecies, S 



no otlicrs, but thi- 'iil<'. and the absence of 



•i ihe pita confirm this conclusion. These series, therefore, <*:m be 



with the more normal species of the caloceran scries, in 



which the qundrn^on il form of whorl and it- correlated characters played a promi- 



i tidaB " ere 



1 and tubercn mal whorls In the development of the 



individual, .1 form anH tub idded 



by | t iiri.u il \ of ephebol 



