170 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



limited time only; and that they do not much in- 

 crease in size afterwards, but remain dwarfed and 

 stunted, all their energy being used in thickening 

 their shells. It seems evident that their existence 

 is of very short duration, as compared with those 

 more fortunate individuals who spend the whole of 

 their lives iu the warm or tropical seas. That none 

 of these Globigerinidse live on the bed of the ocean, 

 I feel convinced, having examined a very great 

 number taken in the deposits from various localities 

 all over the world, both in a fresh and dry condi- 

 tion ; but in no instance have I been able to detect 

 sarcode. I have, however, seen cases where at first 

 I felt almost certain I had discovered sarcode ; but 

 on more minute and closer examination, what was 

 thought to be sarcode turned out to be pale yellow 

 and green glauconitic matter, with some fine argil- 

 laceous, and probably organic, material.* 



Why these heavy Arctic varieties are not com- 

 monly taken in abundance by the tow-nets, or why 

 they are not observed so often with other pelagic 

 animals in the Arctic Seas, must be left for future 

 investigations to solve. 



The Globigerinidse found in the deposits of the 

 warm area are exceptionally small. The shells are 

 notably thinner, but they have not the compact, 

 dwarfed, or Arctic peculiarities, which are character- 

 istic of those found in the cold area. From the most 

 minute to the largest specimens, they are all well- 

 formed typical Globigerina bulloides ; on the other 

 hand the Arctic varieties, Globigerina dutertrei and 

 Globigerina pachyderma, are almost entirely wanting. 

 All my observations go to show that both the last- 

 mentioned forms diminish very rapidly in number 



* It may here be noted, and is of importance, that on both sides 

 of the ridge a considerable amount of glaueonite is found in the 

 deposits. Many of the Foraminif era shells, and other organic 

 remains, are found filled with this peculiar mineral ; and after 

 treatment with dilute hydrochloric acid, beautiful and perfect 

 casts of these organisms remain. 



