20 



NATURAL SCIENCE 



[July 



parations and tow-net gatherings made during the Challenger Ex- 

 pedition, the following species of Foraniinifera have been recognised 

 as pelagic : — 



Orbulina univcrsa, d'Orbigny. 

 Hastigerina pelagiea (d'Orbigny). 

 Pullenia obliquilocidata, Parker and Jones. 

 Sphaeroidina dehiscens, Parker and Jones. 

 Candeina nitida, d'Orbigny. 

 Cymbalopora ( Tretomphalus) bulloides 



(d'Orbigny). 

 Pulvinulina menardii (d'Orbigny). 



,, iumida, Brady. 



,, canariensis (d'Orbigny). 



,, micheliniana (d'Orbigny). 



,, crassa (d'Orbigny). • 



,, patagonica (d'Orbigny). 



Cymbalopora bidloides 1 (Fig. 3) can hardly be regarded as a true 

 pelagic Forarninifer. It was only captured in the neighbourhood 

 of coral reefs, and the curious thing about it is that not a single 

 specimen was taken containing ordinary sarcode, similar to that 

 observed in the other species of pelagic Foraminifera. In all the 

 specimens the shells were filled with immense numbers of minute 

 zoospores ; these latter spread over the field of the microscope in a 

 cloud-like swarm when a shell was broken under the cover-glass. 



The usual colour of the sarcode of the pelagic Foraminifera is-- 

 yellowish-brown. In Hastigerina it is bright red from the presence 

 of red coloured oil-globules and pigment. This red colour enabled 

 me to pick up this species with a beaker on the sea-surface more 

 easily than other species. In Globigerina bulloides (hirsuta) and 

 aequilateralis the yellow-orange colour of the sarcode is due to the. 

 presence of numerous oval-shaped xanthidise, or ' yellow cells,' 

 similar to those found in the Radiolaria. When the sarcode with 

 these ' yellow cells ' flows out of the foramina, and mounts between 

 the numerous spines outside the shell, the whole presents a very 

 striking object under the microscope ; the transparent sarcode can 

 be seen running up and down the long silk-like spines, and the 

 ' yellow cells,' seated at the base of these spines, quite obscure the 

 body of the shell. 



The majority of the species in the above list occur within the 

 tropics, and the thick-shelled species occur only in warm water, such 

 as Sphaeroidina dehiscens, Pulvinulina menardii (Fig. 4), Pullenia 

 obliquilocidata, Globigerina conglobata and saccidifcra. The number of 

 species becomes less in the temperate regions, Pulvinulina michelini- 

 ana and canariensis, Orbulina universa (Fig. 2), Globigerina bidloides 

 and injlata being the prevailing forms. In the Arctic and Antarctic 



1 See Narr. Chall. Exp., vol. i., pp. 838-9, 1885. 





