4 GOÉS, RETICULARIAN RHIZOPODA OF THE CARIBBEAN SEA. 



The uext and thircl zone may appropriately be desiguated as the region of Rhi- 

 zopods, or the real chalk bottom, as nowhere else in this sea this dass becomes 

 more prevalent and conspicuous in high development of forms and abundance of spe- 

 cimens than here. It usually commences at from 200 to 300 fathoms. Here many 

 denizens of the deep cold area already present themselves, and it is very probable, 

 that a painstaking and prolonged investigation even in this shallow water would bring 

 to light most of the members of the abyssal fauna. 



The constituents of this bottom deposit are chiefly: 



1. Very fine amorphous chalk-ooze together with fragments of various exuviaj in 

 great abundance, forming the bulk of the deposit and causing it to be peculiarly 

 heavy and tough. 



2. A large quantity of small (0,25 mm.) ovoid-shaped bodies, wbose surface is 

 slightly impressed with coarse reticulation. These are composed of tightly compres- 

 sed or aggiutinated chalk-ooze and are of a darker gray hue than the rest of tlie ooze. 

 Unquestionably they have been formed in the intestines of some lower organisms 

 and represent in a small way the coprolites of the cretaceous strata. 



3. Shells of pigmy and young reticularian Rhizopods presenting themselves in 

 great c{uantity and belonging chiefly to Planorbulina, Pulvinulina, Textularia-forraed 

 Bulimina3, Orbiculina, Cornuspira, Miliolina etc. 



4. Larger reticularian Rhizopods often in great abundance, chiefly Nodosarinaj, Glo- 

 bigerina}, Pulvinulina3, Planorbulina^, Textulariaj, Amphistegina, Valvulinas and Lituolina3. 



5. Exuviaä of Molluscs of many descriptions, particularly of the pelagic Ptero- 

 poda : Creseis, Hyalea, Cuvieria etc, besides a number of the inhabitants of the ooze. 



6. Spongia-spicules, but in very limited quantity, as also a few skeletons of 

 radiolarian Rhizopods and of Diatomaceaä; silicious substances being, in general,, very 

 scarce. 



There is also another sort of bottom with Rhizopods met with on the very decli- 

 vities of the banks, where the deposit seemingiy consists of an aggregation of dead 

 corallines, calcareous skeletons and worms-nests, all transformed into rough masses and 

 lumps resembling old hardened mörtar and gravel. This bottom yields a quantity of 

 shell-sand abounding in large and fine Rhizopods. A neaiiy similar formation, but on a 

 more level bottom, was met with by Count de PourtalÉs off Florida and was called 

 after its eminent explorer Pourtales' Plateau (Report by L. Agassiz; Bullet. Mus. Harv- 

 College I. p. 367). This kind of bottom I have provisionally distinguished as Co- 

 ralline-gravel. 



The high development of the reticularian Rhizopods both on this bottora and in 

 the real ooze is remarkable, not being surpassed even by the same forms which are so 

 much admired in the cretaceous and tertiary strata. Nodosarina communis d'Orb. at- 

 tains here a length of 20 mm.; Nod. complanata Defr. the size of a small tingernail, 

 while Orbiculifia, Cornuspira and Miliolina, Discorbina^ Pidvinulina attain a size far 

 superior to those of the littoral zone. Textularia trochus d'Okb. assumes a labyrinthic 

 structure and becomes compressed nearly in the same way as a Cuneolina d'Orb. Large 



