142 FAMILY LITUOLIDA. 



constituting the type distinguished by Messrs. Parker and Rupert Jones as T. irregularis. 

 Thus the tube, which in this type is always adherent, and has a portion of its wall furnished 

 by the surface on which it grows, may dilate into a large pyriform or oval chamber (fig. 6), of 

 which also the surface beneath forms the inferior boundary, and which commonly shows a 

 margined and semioval aperture at the opposite extremity ; and before undergoing this dila- 

 tation the tube may bifurcate, so as to form another similar tube and dilated chamber. Again, 

 from the farthest extremity of the first chamber, another tube may proceed, which again may 

 dilate into a second chamber ; this, in its turn, may put forth another that dilates into a third 

 chamber ; and thus we may have a moniliform series of ovoidal chambers, connected by cylin- 

 drical tubes, with every degree of variation as to the number of the chambers, the relative 

 length of the tubes, and the straightness or curvature of their line of growth (figs. 8, 9, 10). 

 This type was first observed by Cornuel (' Mem. Soc. Geol. France,' ser. 2, torn, iii, pi. iv, 

 fig. 37), who described the moniliform series of chambers as eggs of Mollusks ; but its 

 Foraminiferous nature was recognised by D'Orbigny, who assigned to it the generic name 

 Welhina, which he also applied to a few-chambered, uniserial, curved form oi Nubecularia (^ 87). 

 It may undergo a further modification by an alternation in the direction in which the connecting 

 tubes spring from the chambers ; which gives to the series a loose Textularian character. 



208. It is obvious from the foregoing description of the shell, that the primary form of 

 the sarcode-body is a simple uniform cord or stolon, which may coil itself into a spiral, either 

 horizontall}^ or veilically, or may take upon itself any other direction ; and that this primitive 

 imiformity may give place to a differentiation of two kinds, — the spiral cord either undergoing 

 segmentation, at intervals, by constrictions more or less complete, in such a manner as to show 

 a tendency to the assumption of the Rotalian form, — or enlarging from time to time by the 

 accumulation of sarcode at particular points, so as to become converted into the semblance of 

 a string of beads, more or less closely set together. 



209. Affinities. — ^The uniform undivided spiral tube which constitutes the lowest and 

 simplest form of Trochammina, is obviously allied to the corresponding imperforate spiral of 

 Cornuspira, the difference between them consisting simply in the material of the shell. But 

 in the tendency of this type to attain, either by the segmentation or by the enlargement of its 

 tube, a more or less regular multilocularity of shell, it ranges upwards in a line which may be 

 considered parallel to Nulecularia, and thus comes to present a near approximation both to 

 the simpler and to the more typical forms of Lituola, from both which it differs chiefly in the 

 finely arenaceous texture of its shell. 



210. Geographical Distribution. — We have examples of this type from all seas, arctic, tem- 

 perate, and tropical ; and the simpler of them are found at very considerable depths, the 

 rotaline forms being apparently littoral, and sometimes occurring even in brackish waters. 



211. Geological Distribution . — Simple adherent moniliform Trocliammince, exactly resembling 

 those which are met with at the present day, are found attached to the surfaces of shells 

 occurring in the Chalk, and even in the Oxford Clay ; and the spirilline forms can be traced 

 back through the Gault and Lower Oolite (in which they abound) to the Permian deposits. 



