248 R. J. L. Guppy — Foraminifera of Trinidad. 



There can be no doubt, therefore, that these chalky earths and 

 limestones were formed in the same manner and at the same depths 

 as the chalky muds which are now being formed in many parts of 

 the Atlantic and Pacific Oceans. The siliceous radiolarian earths 

 indicate even a greater depth than the calcareous deposits. Eadio- 

 larian ooze does not exist in the Atlantic, but is found in the Pacific 

 and Indian Oceans at depths of from 2,000 to 4,000 fathoms. Its 

 existence in Barbados therefore suggests the idea that it was formed 

 in a deep basin which was open to the Pacific as well as to the 

 Atlantic, and consequently at a time when the Isthmus of Panama 

 did not exist." 



These conclusions are exactly applicable to the Naparima oceanic 

 beds. But it must be admitted that the enormous amount of change 

 in the physical geography of this portion of the earth's surface 

 which would be required to satisfy these conclusions makes one feel 

 inclined to be contented to accept a less depth of water than that 

 above indicated, if other circumstances can be shown to admit of 

 this. And I think that this can be done ; for the amount of clastic 

 material found in certain of the beds (Nariva Series) betokens (as 

 I may hereafter have an opportunity of showing) nearness of land 

 and a shallower sea than might apparently be indicated by the 

 Microzoic fauna. 



Note on the foregoing Paper. 



Ludwig Rhumbler has (in Nachrichten Gesellschaft der Wtssen- 

 schaften zu Gottingen, 1895, p. 51, and the paper before cited) two 

 very noteworthy papers on the phylogeny of Foraminifera. In the 

 first of these papers he has propounded a very ingenious systematic 

 arrangement of the families. My researches have not enabled me 

 to say how much of his system is founded in fact, but the observations 

 in the foregoing paper show that so far as regards the phylogeny of 

 Nodosaria the system is not exactly applicable. Indeed, it is most 

 likely that all triserial and biserial Foraminifera have been evolved 

 from PolymorpMna, their triserial and biserial nature being in fact 

 due to that parentage, the primordial form being a unicellular 

 PolymorpMna. 



The theory that Nodosaria is derived directly from Lagenn, and 

 that Cristellaria and related forms are derived from Nodosaria, is the 

 result of an idea that complex forms must be evolved from simpler 

 ones, and that a simple form cannot be evolved from a composite one. 

 The fact cannot be denied, however, that in Clavulina, Bigenerina, 

 Uvigerina, etc., the simpler form follows on the more complex one. 



Ehumbler's observations tend, I think, to confirm mine respecting 

 the so-called gemmation or colony-building of Foraminifera. This 

 theory appears to me to be founded on a misconception of the real 

 mode of growth of the foraminifer. The body of the foraminifer, 

 like that of the mollusc, grows by interstitial increase, while the shell 

 is extended by incremental increase. To accommodate the integument 

 to the increase of size, the insect and the crustacean exuviate their old 

 shells and form new ones. But the mollusc and the foraminifer, 



