124 PROTOZOA. 



genera, the specialist will consult special treatises • and it does not 

 appear to be necessary for the wants of ordinary students to do more 

 than to supply a brief statement of the conspicuous characters — 

 especially the differential 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 absolutely uniform plan. 

 In the case, however, of Invertebrate fossils, as being those with 

 which the palaeontologist is more especially called upon to deal, the 

 families of each group will, where possible, be defined, 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, Dr Henry 

 Brady, who has so greatly contributed to our knowledge of this 

 difficult group of organisms. 



The first famity of the old division of the Imperforate Foraminifera, 

 that of the Gromidce, requires no special consideration from a palaeon- 

 tological point of view, as it is not represented by any fossil forms. 

 Most of the Gromidce are inhabitants of fresh waters, and they 

 possess a thin, chitinous, imperforate shell, sometimes encrusted 

 with foreign bodies, and with a general pseudopodial aperture at one 

 or both ends. Owing to the horny character of the shell, it is hardly 

 probable that any members of this family will ever be discovered in 

 the fossil condition. 



In the family of the Miliolidce, the test is opaque, porcellanous, 

 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 Recent period inclusive. One of the simplest forms of this 

 group is Cornuspira (fig. 29, a), in which the shell is a simple un- 

 chambered spiral, like the shell of a Planorbis. The genus is repre- 

 sented for the first time in the Lias, and is found under living forms 

 in our seas. Nubecularia is a still older type, beginning in the Trias, 

 and its test, extraordinarily variable in shape, is usually parasitic upon 

 shells and other foreign bodies. In Miliola, again (fig. 29, b, repre- 

 senting the sub-generic form Quinqueloculina), the shell is still ex- 

 tremely variable in form, but it consists typically (Biloculind) of a 

 series of chambers wound round an axis, in such a manner that each 

 embraces half the entire circumference. This genus dates from the 

 Trias, and is well represented in recent seas. It abounded in Eocene 

 times, one of the Tertiary limestones of the Paris basin being known 

 as the " Miliolite limestone," in consequence of its being largely 

 made up of the shells of a Miliola. In Pe?ieroplis (fig. 29, c), which 

 is closely allied to Cornuspira, the shell is a flattened spiral, which 



