F0RAMIN1FERA. 1 33 



complex and is furnished with a "supplemental skeleton" and " canal- 

 system" (fig. 21). Among the typical Rotaline forms, the genus 

 Discorbina, with its coarsely porous shell, dates from the Chalk, 

 and is found living in our seas. Pulvinulina (fig. 24), on the other 

 hand, with a more finely porous shell, has been detected by Brady 

 in rocks of Carboniferous age, and is thus one of the earliest rep- 

 resentatives of the Rotalines. In Rotalia itself (figs. 21 and 29, <?), 

 the test is also spiral and turbinoid, but its structure is more com- 

 plex than in the preceding, the shell-substance being compact and 

 very finely porous ; while each chamber is enclosed by a complete 

 wall of its own, and there are canal-like spaces between the two 

 lamellae forming each septum. In these respects, Rotalia closely 

 approaches the Nummuline type. The earliest RotalicB appear in 

 the Jurassic, but the genus attains its maximum in the Tertiary 

 period, and is well represented at the present day. The approxi- 

 mation to the Nummuline type is further manifested by Calcarina 

 (fig. 26, b and c), in which the shell is spiral and discoidal, with 

 spur-like marginal appendages, and with a well-developed " supple- 

 mental skeleton " and " canal-sytem." The genus has been shown 

 by Brady to commence in the Carboniferous. In Planorbulina the 

 shell is composed of numerous segments, at first spirally and then 

 cyclically disposed. It dates from the Tertiary period, but the 

 forms which are included under the sub-generic name of Trun- 

 catulina (fig. 29, p) commence in the Carboniferous. Tinoporus, 

 dating from the Chalk, is in some respects intermediate between 

 Calcarina and Planorbuli?ia, its general form being like that of the 

 former, while the irregular and partly cyclical arrangement of its 

 chambers recalls the latter. No " general aperture " is present, but 

 a " supplemental skeleton " and " canal-system " are developed, both 

 of these structures being wanting in the allied Gypsina. Though not 

 known in the fossil condition, the genus Polytre??ia may be alluded 

 to here, since it has some curious resemblances to certain of the 

 Polyzoa. It forms crusts, or, more commonly, branched outgrowths, 

 parasitically attached to foreign bodies ; and it consists of numer- 

 ous intercommunicating irregular chambers, the walls of which are 

 penetrated by an extensive system of capillary canals, a true canal- 

 system being, however, absent. Polytrema seems to be the rep- 

 resentative in the Rotaline series of the singular genus Stacheia 

 among the Imperforata. Lastly, an aberrant type of the Rotalines 

 is constituted by the genus Spirillina, in which the test has the 

 form of a calcareous tube, without any internal partitions, coiled 

 into a flat spiral, and either free or attached to some foreign body. 

 The genus begins in the Tertiary rocks, and is represented by 

 living forms. 



Finally, we have the family of the Nuvimidinidce, comprising the 



