52 MANUAL OF ZOOLOGY. 



not improbable that the large Silurian fossils known as Re~ 

 ceptaculites and Stromatopora shonld really be referred to this 

 order. In the Carboniferous rocks of Russia whole beds are 

 composed of a species of Fusulina. In the Secondary rocks 

 Foraminifera occur in great abundance, the widely-spread for- 

 mation known as the Chalk being crowded with these organ- 

 isms. Chalk itself, in fact, is almost entirely composed of the 

 cases of Foraminifera, some of which are identical with species 

 now existing. 



In the Tertiary rocks the Foraminifera attain their maximum 

 of development, both as regards the size and the number of 

 the forms which characterise them. The period of the Middle 

 Eocene is especially distinguished by a very widely-spread and 

 easily recognised rock known as the Nummulitic Limestone, so 

 called from the abundance in it of a large coin-shaped Fora- 

 minifer, termed the Nummnlite. The Nummulitic Limestone 

 stretches from the West of Europe to the frontiers of China, 

 but in some cases, in place of Nummulites proper, it contains 

 the remains of a mimetic form termed Orbitoides. Upon the 

 whole, Dr. Carpenter concludes that ' there is no evidence of 

 any fundamental modification or advance of the foraminiferous 

 type from the Palaeozoic period to the present time.' 



CHAPTER IV. 

 RADIOLARIA. 



THE order Radiolaria was founded by Miiller to include the 

 folycystma, the Acanthomstrina, and the Thalassicollida, to 

 which Dr. Carpenter adds Actinophrys and its allies, chiefly 

 on account of the form of the pseudopodia. Here, however, the 

 term will be employed to designate the first three of these, 

 and Actinophrys will be placed amongst the Amoelea, to which 

 its alliance appears to be more decided. 



The order Radiolaria may be defined as comprising those 

 Rhizopods which possess a siliceous test or siliceous spiculet, and 

 are provided with pseudopodia which stand out like radiating 

 filaments, and occasionally run into one another. 



I. FAMILY ACANTHOMETRINA. The Acanthometrce are all ma- 

 rine, and consist of sarcode-bodies which are supported by a 

 framework of radiating siliceous spines, the extremities of 

 which usually project considerably beyond the body. The 

 substance of the body admits of division into an outer mem- 



