114 PROTOZOA. 



The first family under this section that of the Lagenida 

 comprises " hyaline " or " vitreous " Foraminifera, with a 

 calcareous shell, the walls of which are pierced by numerous 

 minute pores, and are usually more or less strikingly thin 

 and glassy. In the compound forms of this group the suc- 

 cessive chambers have their posterior walls formed by the 

 front wall of the preceding segment, so that the septa are 

 always single, instead of being double, and there is never 

 any " intermediate " skeleton. The family may be divided 

 into two series, Lagena itself being the type of the one, 

 while Nodosaria is the type of the other. In Lagena (fig. 

 18, /) the shell is simple, flask-shaped, unilocular, with a 

 single prominent aperture. The genus commences in the 

 Carboniferous, with a few rare forms, is further developed in 

 the Secondary and Tertiary, and is well represented at the 

 present day. Polymorpliina (fig. 18,y) is allied to Lagena, 

 but it is multilocular, the chambers being usually arranged 

 in a double series. It is represented in the Trias, and sur- 

 vives under common types at the present day. In the series 

 of which Nodosaria is the type, we have perforate Forami- 

 nifera consisting of a succession of chambers, each of which 

 is essentially similar to a Lagena, arranged in a series, which 

 is usually nearly or quite straight, though sometimes spirally 

 involuted. In Nodosaria itself (fig. 18, g) the chambers are 

 simple, and are disposed in a straight line. It ranges from 

 the Permian to the present day. Dentalina, ranging from 

 the Carboniferous onwards, is fundamentally like Nodosaria, 

 but the shell is bent like a bow. Vagimdina comprises 

 forms similar to Nodosaria, but laterally compressed, and 

 begins in the Trias. Marginulina (fig. 18, Ji) is slightly 

 curved, or is sometimes crosier-shaped, and also starts in the 

 Trias. Frondicularia (fig. 18, i) has the shell flattened out 

 and leaf-like, and likewise makes its first appearance at the 

 summit of the Trias. Lastly, Cristellaria (with Eobulina} 

 comprises forms more or less spirally inrolled or crosier- 

 shaped, which extend from the Chalk to the present day, 

 and have a very wide development both individually and 

 specifically. 



In the second family of the Perforate Foraminifera that 



