240 GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION. 



Foraminifera, whence it would appear that, of some seven hundred 

 recognised species, the range of not less than three hundred and 

 thirty-eight extends as far back as the Tertiary period ; of one hun- 

 dred and twelve to the Cretaceous ; fifty-six to the Oolite ; forty-one 

 to the Lias; sixteen to the Trias; eight to the Permian; six to the 

 Carboniferous (Haplophragmium agglutinans, Ammodiscus incer- 

 tus, A. gordialis, Truncatulina lobatula, and the two Silurian forms) ; 

 two to the Devonian (also Silurian) ; and two to the Upper Silurian 

 (Lagena laevis and L. sulcata). A number of other doubtful forms 

 occurring fossil may perhaps also be referred to the category of 

 recent equivalents, as, for example, the Girvanella, described by 

 Nicholson and Etheridge from the English Silurian deposits, which 

 not improbably is the recent Hyperamina vagans. 



CORALS. 



The more important corals of the present day belong to the 

 groups Zoantharia and Alcyonaria, the former of which, frequently 

 designated the six-tentacled corals (Hexacoralla), embrace the naked 

 sea-anemones (Actiniae), and nearly all the familiar stone-corals, and 

 the latter (Octocoralla, eight -tentacled corals), the sea-pens, sea- 

 shrubs, red-coral, and organ-pipe. In the group of the comb- 

 bearers (Ctenophora) are comprised a limited number of forms, 

 Beroe, Venus's girdle, &c., which are entirely destitute of a coral- 

 lum, and in many essential points of structure depart widely from 

 the other members of the class. A fourth division, the rugose 

 corals (Rugosa or Tetracoralla), which, in the early periods of the 

 earth's history, constituted such a marked feature in the successive 

 faunas (Silurian, Devonian, Carboniferous), are limited at the pres- 

 ent day, as far as our existing knowledge goesj to possibly not more 

 than two generic types, Guynia, from the Mediterranean and the 

 Gulf of Mexico, and Haplophyllia, from the coast of Florida. 



The sea-anemones are, collectively, cosmopolitan in their distri- 

 bution, and inhabit the sea to very nearly the profoundest depths 

 that have thus far been reached by the dredge, although, both as 

 regards specific and numerical development, they more distinctively 

 characterise the littoral and laminarian zones. The deep-sea species 

 are, however, not exactly scarce, and it would appear, from the 

 "Challenger" observations, that the numerical decrease corre- 

 sponding to the increase in depth is not nearly as great as might 



