CHAPTER VI. 



OF THE FAMILY LITUOLIDA. 



205. The series of generic forms which there seems reason for bringing together under 

 the family designation Lituolida, is distinguished from all other types of Foraminifera by 

 this circumstance, — that whereas we find both in the porcellanous and m the vitreous series 

 that the individuals of particular genera occasionally exhibit an arenaceous incrustation, this 

 is simply an addition to the calcareous shells proper to their respective types, and is not a 

 substitute for it, — whilst in these arenaceous types the investment of the body, although 

 presenting the regular conformation of a calcareous shell, is really a " test " composed of an 

 aggregation of particles obtained from external sources, the organic cement by which these 

 particles are united being all that is furnished by the animal. The group thus constituted 

 includes a wide range of forms, of which a large proportion have been associated, by the 

 systematists who have treated of them, with the genera of the vitreous series to which they 

 respectively seemed most nearly alHed. But, as already pointed out {% 75), the affinities of 

 the purely arenaceous types are essentially with the porcellanous series, since their animals 

 can only put forth their pseudopodia from the terminal aperture ; and they are also allied in 

 the relatively large size of that aperture, in the mode in which the new chambers are added 

 to the preceding even in the highest forms, and in the incompleteness of the testaceous enve- 

 lope in those humbler forms which attach themselves, like Nubectdarice, to the surfaces of other 

 bodies, and are dependent upon these for part of their protection. It is not improbable that 

 future research may add largely to our knowledge of these arenaceous forms, the special 

 study of which has hitherto been prosecuted only by Messrs. Parker and Rupert Jones. At 

 present they appear referable to three generic types ; of M'hich the first, Trochammina, starts 

 from a rank parallel to that of Cornmpira in the porcellanous, and of Spirillina in the vitreous 

 series, but has a much wider range of variation in form, and the cavity of which, though origi- 

 nally unilocular, not unfrequently becomes multilocular by the formation of imperfect septa ; 

 the second, Liluola, closely corresponds with Nubccidaria in its lower adherent forms, but 

 ranges in its higher free forms with the " spirilline '' variety of PenerojjUs, and, in the sub- 

 division of its principal chambers presents a rude sketch of OrlicuUna; whilst the third, 

 Valvulina, presents features of approximation to certain occasionally arenaceous types of the 

 vitreous series, not merely in a very close similarity of external configuration, but also in the 

 primary investment of its body by a thin lamina of shell formed upon the perforated vitreous 

 type, which is subsequently covered-in by a layer of arenaceous cement-substance, so as to be 

 rendered actually imperforate. 



