192 DR. CARPENTER'S RESEARCHES ON THE FORAMINIFERA. 



ficial cells, a character to which the more extended knowledge of this type has made 

 it clear to me that not the slightest value is to be attached (see Sect. IV.). I showed 

 that in one as in the other, the cells are normally closed-in over the whole surface; 

 that the cells of the two surfaces are separated from each other by an intervening 

 stratum, traversed by a set of round cells or passages of its own, with which each 

 superficial cell communicates by two small apertures ; and that the only real exter- 

 nal orifices are the minute pores at the margin of the disk, which communicate, not 

 directly with the cells of the superficial layers, but with the passages of the inter- 

 mediate stratum. 



7. A very important addition to this limited measure of information was made not 

 long afterwards by Professor WILLIAMSON of Manchester, who, in a paper read before 

 the Microscopical Society of London, June 12, 1850, and published in its Transac- 

 tions (First Series, vol. iii. March 1851), first gave a minute description of the small 

 recent Orbitolites marginalis of LAMARCK (which, however, he designated as O, com- 

 planata); contrasted it with that of a large recent Orbitolite from Tonga, shown by 

 his description to be identical with the Marginopora of QUOY and GAIMARD, to my pre- 

 vious account of which he added some important particulars ; and compared both 

 with the well-known Orbiculina adunca of the Bahamas. His investigations led him 

 to the conclusion, that these three forms should rank under the same genus Orbi- 

 culina; their most important structural features being common to all, whilst their 

 differences are only of specific value. His Orbiculina complanata (really Orbitolife-s 

 marginalis) he characterizes by its spiral commencement, and by its possessing only 

 one layer of cells ; his O. Tonga (Marginopora) he characterizes by its cyclical com- 

 mencement, and by its possession of two superficial layers of cells, with an interme- 

 diate stratum, as I had previously pointed out; whilst the O. adunca he shows to 

 commence on the spiral type, and to carry it on much further than his O. compla- 

 nata, but finally to assume the cyclical, and then to correspond very closely with his 

 O. Tonga. The title of the genus Orbitolites to a place in the group of Foraminifera, 

 in near proximity to, if not in union with, Orbiculina (which had been ranked as such 

 by M. D'ORBIGNY from an early period of his investigations), and the entire absence 

 of any ground for ranking it among the Bryozoa (Polyzoa), were clearly established 

 by Professor WILLIAMSON in this valuable memoir; and though I shall hereafter have 

 occasion to show that some of his conclusions were erroneous, yet I regard them as 

 fully justified at the time, by the information which the materials at his command 

 afforded ; my own means of correcting them being only supplied by the comparison 

 I have been enabled to institute through a much wider range of specimens. And it 

 is with great satisfaction that I am enabled to add, that, after a careful inspection of 

 my preparations and drawings, Professor WILLIAMSON authorises me to express his 

 full accordance in the results which I shall now proceed to detail. 



8. As the value of such details cannot be truly estimated without some knowledge 

 of the range of the observations from which they are derived, I think it right to state 



