552 DE.-W. B. CAEPENTEE ON OEBITOLITES TENUISSIMA. 



sub-segments (formed by the division of the principal segments) at every new stage 

 of gemmation ; so that at last the aloe of the spire, extending themselves on either 

 side round the nuclear mass, meet and complete the circlet, around which new zones 

 are then successively budded forth, as in the forms that are cyclical from their com- 

 mencement. 



I did not at that time feel justified in calling in question the validity of the order 

 Cyclostegues, which had been instituted by M. D'OKBIGNY, for the reception of this 

 and other types characterised by the cyclical plan of growth ; but in my Second 

 Series (presented in the following year), which contained the results of a similar 

 investigation of the geims Orbiculina, I showed that the latter always begins life on 

 the spiral plan of growth, which may or may not give place subsequently to the 

 cyclical, and that the marginal portions of a full-grown cyclical Orbiculina cannot 

 be distinguished from similar portions of an Orbitolite. From this fact I drew 

 the conclusion* that although Orbitolites and Orbiculina had been placed by 

 M. D'ORBIGNY in two distinct orders, Cyclostegues, and Helicostegues, " the relation- 

 ship between them must be extremely close ; " and ventured further to affirm that 

 no Classification can have any claim to be considered as natural, in which they shall 

 be widely separated." 



To this point I reverted in the Concluding Summary appended to my Fourth 

 Memoir,t in which I showed how completely the results of my researches were opposed 

 to the principles on which the Classification of M. D'ORBIGNY had been framed, 

 indicated the line of " descent with modification " by Avhich a division of the 

 primary segments that form the simply-chambered shell of a Peneroplis into sub- 

 segments would give origin to the chamberlets of the spiral Orbiculina, and pointed 

 out how gradational the transition is from the latter to the cyclical Orbitolites. 



When I subsequently undertook, in conjunction with my friends, W. K. PARKER and 

 T. RUPERT JONES, to frame an entirely new Classification of FORAMINIFERA on the 

 basis of the principles I had laid down, I felt no difficulty in assenting to their view 

 that the pedigree of this series might be traced yet further back, viz. : to those simplest 

 forms of the Milioline type, whose shell is a flattened nautiloid spire altogether 

 destitute of partitions thus belonging to that monothalamous section which all 

 previous Systematists had ranked as fundamentally distinct from the polythalamous. 

 "From the undivided spiral of Cornuspira" I pointed out ("Introduction to the 

 Study of the Foraminifera," p. 67), "to the regular scarcely-divided spiral of certain 

 ' spiroloculine ' forms of Miliola, the transition is almost insensible ; and from 

 the 'spiroloculine' we pass by easy steps to all the other forms of .the Milioline 

 type." Again, a subdivision of the widely-expanded spire of Cornuspira into 

 segmental chambers gives us Peneroplis, with its septal planes perforated by a row of 

 separate pores ; while from this, it was again pointed out, the spiral Orbiculina might 



* Phil. Trans., 1856, p. 552. 

 t Ibid., 1860, p. 571. 



