ROTALIA 



825 



long 



divide the chambers being in the best developed examples composed 

 of two laminae, and spaces being left between them which give 

 passage to a system of canals whose general distribution is shown 

 in fig. 624. The proper walls of the chambers, moreover, are 

 thickened by an extraneous deposit or ' intermediate skeleton,' which 

 sometimes forms radiating outgrowths. This peculiarity of conforma- 

 tion, however, is carried much further in the genus < '/ilcnriiHi. which 

 has been so designated 

 from its resemblance to a 

 spur-rowel (fig. 629). The 

 solid club-shaped append- 

 ages with which this shell 

 is provided entirely be- 



to the ' intermed i ; 1 1 < 

 skeleton ' b, which is quite 

 independent of the cham- 

 bered structure a ; and this 

 is nourished by a set of 

 i -1 1 1 als containing prolonga- 

 tions of the sarcode-body 

 which not only fin-row the 

 surface of these appendages, 

 but are seen to traverse 

 their interior when this is 

 laid open by section, as 

 shown at c. In no other 

 recent foramiiiifer does the 

 ' canal system ' attain a like 

 development ; and its dis- 

 tribution in this minute 



shell, which has been made out by careful microscopic study, affords 

 a valuable clue to its meaning in the gigantic fossil organism 

 Eozooti canadense. The resemblance which Calcarina bears to the 

 radiate forms of Tiitnj>nrns (fig. 623), which are often found with 

 them in the same dredgings, is frequently extremely striking ; and 

 in their early growth the two can scarcely be distinguished, since 

 both commence in a ' Rotaline ' spire with radiating appendages ; 

 but whilst the successive chambers of Cdlcur'nni continue to be 

 added on the same plane, those of 'rimi/im-i/* are heaped up in less 

 regular piles. 



Certain beds of Carboniferous limestone in Russia are entirely 

 made up, like the more modern Nummulitic limestone, of an aggre- 

 gation of the remains of a peculiar type of Foraminifera, to which 

 the name Fusulina (indicative of its fusiform or spindle-like shape) 

 has been given (fig. 625). In general aspect and plan of growth it 

 so much resembles Alveolina that its relationship to that type would 

 scarcely be questioned by the superficial observer. But when its 

 mouth is examined it is found to consist of a single slit in the 

 middle of the lip ; and the interior, instead of being minutely 

 divided into chamberlets, is found to consist of a regular series of 

 simple chambers ; while from each of these proceeds a pair of 



FIG. 624. Section of Hotalia Schroefericma near 

 its base and parallel to it, showing, , a, the 

 radiating interseptal canals ; b, their internal 

 bifurcations ; c , a transverse branch ; d, tubulated 

 wall of the chambers. 



