CARPENTER ON THE STUDY OF THE FORAMINIFERA. 339 
as Dr. Carpenter has shown in the annexed table, affords the means 
of indicating representative groups within the limits of the Porcel- 
lanous and the Vitreous series respectively:— 
Porcellanea. Vitrea. 
Simple complanate spiral 
Spiral, with the chambers subdivided 
into chamberlets 
Cyclical, with annuli subdivided into 
chamberlets . 
Spiral, with elongated axis, chambers 
subdivided into chamberlets 
Peneroplis. Opereulina. 
Orbiculina. Heterostegna. 
Orbitolites. Cycloclypeus. 
Alveolina. Pusulina. 
Cornuspira , in like manner, represents the vitreous Spirillina and 
the aranaceous Trochammina. 
The inadmissibility of the Polythalamia as a separate group, is at 
once proved by the fact that their sole distinctive feature does not 
correlate with any other worth insisting on ; for Polythalams differ 
among themselves, as do Monothalams, in characters of such impor¬ 
tance as the perforation and non-perforation of the shell, its texture, 
and the nature of its perforations, when present. What these differ¬ 
ences imply, we have already endeavoured to show. The general 
analogy of Zoology plainly enough demonstrates, that the power of 
multiplying by continuous gemmation, however interesting from a 
physiological point of view, is, in most cases, too variable a character 
to be of any value to the systematist. With regard to the Foremini- 
fera in particular, this question has been set at rest by the discovery 
of three polythalamous genera,— Dactylopora , Acicularia , and Globi- 
gerina, in which the separate shell-chambers do not communicate with 
one another internally. In Carpenteria all the chambers open into a 
common vestibule. That the passage from Monothalamia to Poly¬ 
thalamia is, in truth, a gradual one, is further indicated by the exist¬ 
ence of what Dr. Carpenter terms potentially polythalamous* forms, 
which, though actually monothalamous, have the power of indefinite 
shell-growth. Thus, in one family, Miliolida , the following gradations 
may be pointed out. 
1. True Monothalamia.— Squamulina. 
2. Monothalamia with indefinite growth.— Cornuspira. 
3. Monothalamia (?), in which irregular chambers are foreshadowed. 
—JSTubecularia ; Vertebvalina. 
4. Polythalamia, with large chambers, separated only by constric¬ 
tions. — Miliola. 
5. Polythalamia with true septa.— Peneroplis. 
6. Polythalamia with milioline chambers, irregularly sub-divided.— 
Pabular ia. 
7. Polythalamia with true septa, and chambers subdivided into 
chamberlets.— Orbiculina; Alveolina; Orbitolites. 
* See Natural History Keview, October, 1861, p. 468. 
N. H. B.—1863. ’ 2 A 
