108 PROTOZOA. 



may seem to demand mention on the ground of their being 

 common, or in other respects, geologically or zoologically, of 

 peculiar importance. For anything like a complete list of the 

 known structural types of each group, or the characters of 

 the recorded genera, the specialist will consult special treat- 

 ises ; and it does not appear to be necessary for the wants of 

 ordinary students to do more than to supply a brief state- 

 ment of the conspicuous characters especially the differen- 

 tial characters of the more widely distributed and more 

 important types in each group. Nor can even this limited 

 characterisation of leading types be carried out with equal 

 fulness in the case of all groups of fossils, or upon any abso- 

 lutely uniform plan. In the case, however, of Invertebrate 

 fossils, as being those with which the paleontologist is more 

 especially called upon to deal, the families of each group will, 

 where possible, be denned, and some of the chief generic 

 types will be noticed. The subjoined engraving, representing 

 some of the principal type-forms of the Foraminifera, is from 

 a drawing kindly made for the author by his friend, Mr Henry 

 Brady, F.R.S., who has so greatly contributed to our know- 

 ledge of this difficult group of organisms. 



IMPERFORATE FORAMINIFERA. Among the Imperforata, we 

 have the three families of the Gromida, Miliolida, and Litu- 

 olida, of which the first needs no notice, as being quite 

 unknown in the fossil condition. 



In the family of the Miliolida, the test is opaque, porcel- 

 lanous, unilocular, or multilocular, and extremely variable in 

 shape ; the oral aperture being simple and undivided, or being- 

 formed by numerous pores. The family, as far as known at 

 present, is not represented in the Palaeozoic period, but ranges 

 from the Trias to the Kecent period inclusive. One of the 

 simplest forms of this group is Cornuspira (fig. 18, a\ in 

 which the shell is a simple unchambered spiral, like the shell 

 of a Planorbis. The genus is represented in the early Ter- 

 tiary, and is found under living forms in our seas. Nubecu- 

 laria is a much older type, beginning in the Trias, and its 

 test, extraordinarily variable in shape, is parasitic upon shells 

 and other foreign bodies. In Miliola, again (fig. 18, &, 

 representing the sub-generic form Quinqueloculina), the shell 



