552 DR. W. B. CARPENTER ON ORBITOLITES TENUISSIMA. 
sub-segments (formed by the division of the principal segments) at every new stage 
of gemmation ; so that at last the alee 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. 
1 did not at that time feel justified in calling in question the validity of the order 
Cyclostegiies, which had been instituted by M. D’Orbigny, 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 genus Orbieulina, 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 Orbieulina cannot 
be distinguished from similar portions of an Orbitolite. From this fact I drew 
the conclusion* that although Orbitolites and Orbieulina had been placed by 
M. D’Orbigny in two distinct orders, Cyclostegiies, 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,! 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 which 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 Orbieulina, 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 Orbieulina might 
* Phil. Trans., 1856, p. 552. 
t Ibid., 1860, p. 571. 
