Manchester Memoirs, Vol. xlviii. (1904), No. 5. 23 



Orbitolites duplex, Carpenter. 



Orbitolites duplex, Carpenter ('83), p. 25, pi. 3, figs. 8-14; 

 pi. 4, figs. 6-10 ; pi. 5, figs. i-io. 



The specimens are small and seldom exceed one- 

 eighth of an inch in diameter. The double row of pores 

 shows distinctly on the edge of the disk. These pores 

 lie in depressions, but the ridges between them are not 

 developed as in the typical form. The upper and lower 

 rows of pores do not lie opposite one another but 

 alternate. Carpenter ('83, p. 43) in his "concluding 

 summary, with a study of the theory of descent " of the 

 Orbitolites, states, ^^ First, that the remoter ancestry, instead 

 of being indicated (as it commonly is in the developmental 

 history of the higher organisms) by obscure and transitory 

 phases, is here distinctly represented in the earlier stages of 

 the completed form. Thus, if the development of a very 

 young Orbitolites tenuissima were checked in its early 

 Milioline stage it would be accounted a Spiroloculina ; if 

 checked in its short - Peneropline stage, it would be 

 accounted a true Peneroplis; and if checked in itsOrbiculine 

 stage, it would be accounted a true Orbiculina. And so, 

 if the development of the "sub-typical" variety of 

 Orbitolites complanata were checked in its first stage, it 

 would rank as Orbitolites marginalis ; if checked in its 

 second, as an Orbitolites duplex ; and if checked in its 

 third, as the earlier (fossil) form of Orbitolites complanata." 



This shows the difficulty that arises in attempting to 

 separate specimens into their respective species. Frequent. 



