GENUS LITUOLA. 143 



Genus II.— Lituola (Plate VI, figs. 39—47, and Plate XI, figs. 1 1—14). 



212. History. — The genus Lituola-^^% instituted by Lamarck (in the first instance, lviii, 

 under the designation LifuoJites), for the reception of a minute crozier-shaped shell, common 

 in the Cretaceous formation, which, resembling SpiroUna (that is, the spiroline variety of 

 Pencroplis) in external form, differs from it in having its principal chambers subdivided by 

 secondary septa into chamberlets. The genus has been adopted in its original sense by 

 D'Orbigny and most other systematists ; but the recent inquiries of Messrs. Parker and 

 Rupert Jones (lxxix, lxxxi) have led them greatly to extend the application of this generic 

 designation, and to bring under it a wide range of forms, which not only agree with each 

 other in the peculiar composition of the shell, but are so closely linked together by continuity 

 of varietal modifications in all their differential characters, as to evince the intimacy of their 

 essential relationship. 



213. External Characters. — The shell, in all the forms that liave now to be described, is 

 coarsely arenaceous ; the particles of sand (which may be f ither calcareous or siliceous) being 

 always large enough to be readily distinguished under a moderate amplification, and generally 

 giving a very perceptible roughness to the surface. Sometimes, however, the larger particles 

 are imbedded in a kind of mortar, which, as in the case of TrocJtawmina (^207), seems to be 

 composed of finer particles, drawn from the like source, united by an adhesive exudation from 

 the animal (Plate VI, fig. 42) ; and the shell is then very thick and clumsy, deriving its 

 massiveness, however, entirely from the aggregation of foreign material, and in no degree 

 (like the arenaceous varieties of Nubectdaria and Miliold) from an abundance of the proper 

 shell-substance. In other cases, again, the larger arenaceous particles are fitted together in 

 a very regular manner, without the intervention either of smaller particles or of calcareous 

 cement (Plate VI, fig. 41) ; so that it would seem as if the animal of Lituola had no power 

 whatever of excreting calcareous matter for the consolidation of its envelope, but was altogether 

 dependent for its protection upon its power of drawing to itself and of cementing together 

 the materials brought to it by the ocean-waters amid which it lives. In its simplest form 

 (Plate XI, fig. 11) Lituola is a mere string of suboval, plano-convex, successively enlarging 

 chambers, more or less irregular in outline, attached by their flat side (which is usually 

 imperfect) to the surface of shells, corals, &c. ; and so closely resembling certain forms of 

 Trochammina, as, like them, to have been first supposed by Cornuel (' Mem. Soc. Geol. France,' 

 ser. 2, torn, iii, pi. iv, fig. 36) to be eggs of Mollusks. These two types, however, are readily 

 distinguished by the texture of their shells. Very frequently this series of chambers com- 

 mences in the form of a spiral coil (Plate XI, fig. 12), though it afterwards extends itself recti- 

 linearly or irregularly ; and this is the type which has received from M. D'Orbigny the desig- 

 nation of Placopsilina cenoinana, under which it has been figured by Reuss (lxxxviii). 

 These adherent Placopsiline forms are often wild in their growth, spreading and bifurcating 

 with great irregularity (Plate XI, fig. 14) and to a considerable extent, so as even to attain an 

 inch in length. The spire, however, may continue to develope itself after a regular fashion, 

 so that the shell (still adherent by its flat, and usually imperfect side) has very much the 



