516 



POEAMINIFERA. — ORBITOIDES. 



In the upper and lower walls of these last, minute punctations 

 may be observed, which seem to be the orifices of connecting 

 Tubes whereby they are perforated. The relations of these two 



Fig. 2C4. 



Vertical Section of Orbitoides Fortisii, showing the large Cen- 

 tral chamber at a, and the Median layer surrounding it, covered 

 above and below by the Superficial layers. 



kinds of structure to each other are made evident by the exa- 

 mination of a vertical section (Fig. 264) ; which shows that the 

 portion a, Figs. 262, 263, forms the Median plane, its con- 

 centric circles of Chamberlets being arranged round a large 

 central chamber a, as in Gycloclypeus ; whilst the Chamberlets of 

 the portion b are irregularly superposed one upon the other, so as 

 to form several layers which are most numerous towards the centre 

 of the disk, and thin-away gradually towards its margin. The 

 disposition and connections of the Chamberlets of the Median 

 layer in Orbitoides seem to correspond very closely with those which 

 have been already described as prevailing in Cycloclypeus ; the 

 most satisfactory indications to this effect being furnished by the 



Siliceous casts to be met 

 with in certain Green Sands, 

 which afford a model of the 

 Sarcode-body of the animal. 

 In such a fragment (Fig. 265) 

 we recognize the Chamberlets 

 of three successive zones, 

 a, a', a", each of which seems 

 normally to communicate by 

 one or two passages with the 

 Chamberlets of the zone in- 

 ternal and external to its 

 own ; whilst between the 

 Chamberlets of the same zone 

 there seems to be no direct 

 connection. They are brought 

 into relation, however, by 

 means of Annular Canals, 

 which seem to represent the Spiral canals of the Nummulite, and 

 of which the Internal Casts are seen at b. b, b' b', b" b" . 



396. A most remarkable Fossil, referable to the Foraminiferal 

 type, has been recently discovered in Strata much older than the 



Siliceous cast of portion of Median 

 plane of Orbitoides Fortisii, showing at 

 a a, a' a', a' 1 a', six Chambers of each 

 of three zones, with their mutual com- 

 munications ; and at b b, b' b', b" b", 

 portions of three Annular Canals. 



