PART ni. 



QEOORAPHIGAL AND GEOLOGICAL DISTRIBUTION. 



The present and past distribution of individual animal groups. — Foraminifera. 

 — Corals. — Brachiopoda. — Mollusca generally. — Crifttacea. — Inseota. 



FOKAMOirFEBA. 



Despite the simplicity of their organisation, and their apparent 

 ready adaptability to the most varied phases of existence, it ap- 

 pears that the distribution of these animals is influenced, although 

 perhaps to a less degree, by much the same conditions which 

 govern the distribution of higher forms. While practically the 

 class is of world-wide distribution, and cosmopolitanism — at least 

 among groups of supra-specific value (genera, &c.) — the rule rather 

 than the exception, yet the influence of special conditions, as per- 

 taining to different sections of the earth's surface, is markedly 

 manifest. Thus, we find that in the warmer regions of the globe 

 the foraminiferal fauna, as compared with the corresponding fauna 

 of the regions lying to the north and south, is very much richer 

 both as regards specific and individual development ; and, further, 

 that it comprises a disproportionately large number of forms char- 

 acterised by unusual size and structural complexity (Orbiculina, 

 Orbitolites, Cycloclypeus, Tinopora). Of some seventy or more 

 genera of Foraminifera calcarea recognised by Butschli,^' thirty- 

 eight, or about one-half, are wanting in the Arctic seas, twenty- 

 five are wanting in the British and North seas, and fifteen in the 

 Mediterranean ; on the other hand, all the Arctic and north tern- 



