562 DR. CARPENTER'S RESEARCHES ON THE FORAMINIFERA. 



ton and of a canal-system between the contiguous walls of adjacent chambers, and in 

 the minutely-tubular structure of the shell, all of them points of high physiological 

 importance, Cycloclypeus differs entirely from Orbitolites, and agrees with Nummu- 

 lites ; whilst it agrees with Orbitolites, and differs from Nummulites, in the single 

 circumstance that its mode of increase is cyclical instead of helical, a difference 

 which we have seen to present itself at two different periods of life of the very same 

 specimens of Orbitolites and Orbiculina, and which must, therefore, be a character of 

 quite subordinate importance. 



Genus HETEROSTEGINA. 



111. The correctness of the views just advanced is fully borne-out by the occur- 

 rence of a type, which bears precisely the same relation to Cycloclypeus, that Orbicu- 

 lina bears to Orbitolites; one, namely, in which the form and connexions of the 

 individual chambers, the minute structure of the shell, and the distribution of the 

 canal-system, being essentially the same the plan of growth is helical, at least 

 during the earlier period of life. This is the case with the genus Heterostegina, 

 which was established by M. D'ORBIGNY in his memoir of 1825, but the essential 

 structure of which he has altogether misapprehended. In his latest classification of 

 the Foraminifera*, he ranks this genus in his order Entomostegues, which is com- 

 posed of Foraminifera, whose segments are disposed in a spiral, but in two different 

 planes alternating with each other, so as to render the entire shell inequilateral. 

 Of the genus Heterostegina, which he ranks in close approximation to Amphistegina, 

 he gives this definition : " Coquille a spire embrassante, dont les loges sont sepa- 

 rees inte"rieurement par des cloisons trans versales." Now in the first place, I am 

 quite satisfied that the chambers of Heterostegina do not alternate one with another, 

 but are arranged in one plane about the same axis, as is shown in figs. 1, 7, Plate 

 XXXI.; and secondly, it gives by no means a correct idea of its structure, to liken its 

 chambers to those of Amphistegina save for their division by transverse partitions. 



112. I have had the opportunity of examining, by the kindness of Mr. CUMING, a 

 very extensive series of specimens of this genus (belonging, apparently, to the species 

 H. costata, D'ORB.^), from the Philippine islands ; many of these are of large size, 

 attaining as much as half an inch in diameter ; and the appearance of the adult speci- 

 mens scarcely differs less from that of the young (which latter are alone figured by 

 M. D'ORBIGNY), than it does in the case of Orbiculina. The dredgings of Mr. JUKES 

 have furnished me with numerous specimens of Heterostegina from the Australian 

 coast ; these closely correspond with the figures of M. D'ORBIGNY, being of compara- 

 tively small size, and not exhibiting that peculiar mode of development which is 

 characteristic of the adult. As the Australian forms correspond precisely with the 

 young of the Philippine, there can be no doubt of their specific identity. I recognise 

 the shells of the same species as almost the sole components of a fossilized deposit, 



* Cours 61ementaire de Paleontologie, torn. ii. p. 201. t Foram. Foss. de Vienne, p. 212. 



