178 Messrs. W. K. Parker and T. R. Jones on the 



bigny for the outspread many-celled varieties of Nautilus farctus*. 

 The common Truncatulina lohatula, Walker, is a simple form of 

 this type, arrested, as it were, in its development ; and many of 

 the little so-called Rosalintje, RotalincB, Anomalince, and Planu- 

 lincE, are equally simple dwarf forms ; their relative vcsicularity 

 Qr complanation being due to accidental style of growth and 

 place of attachment, whether it be sea-weed, rough or smooth 

 shell, or other substance. The depth of water, also, and cha- 

 racter of the sea-bottom affect the growth of these very variable 

 shells. Every collector knows the T. lohatula, with its white 

 plano-convex shell, crenulate outline, slit-like aperture, and 

 coarse perforations. Similar features, modified, characterize 

 Nautilus farctus ; this, however, is differentiated by some amount 

 of limbation on the convex face, and by the greater height of the 

 chambers. Plano7'biiJina nitida, D^Orb. (Modeles, No. 78), is a 

 similar form to the last mentioned, not markedly limbate, and 

 having more chambers. PL Mediterranensis, D'Orb. (Ann. Sc. 

 N. vol. vii. p. 280, pi. 5. figs. 4-6 ; and Modeles, No. 79), pre- 

 sents a further developmental step in the growth of these in- 

 structive varieties ; for here we find the same morphological 

 plan, with an increase of chambers, in a delicate and scale-like 

 shell. In PL vidguris, D^Orb. (For. Cuba, pi. 6. figs. 11-15), we 

 have a coarser and somewhat biconvex shell, with a wilder mode 

 of growth. The chambers become baggy and divergent, and 

 present supernumerary lipped apertures. The more irregularly 

 constructed shells of PL vulgaris, whether heaped into a little 

 racemous mass, or ringing the smooth stems of sea-weeds, 

 have been denominated Acervulince by Schultze. Arrested con- 

 ditions of this biconvex variety constitute the Anomalina of 

 D^Orbigny: amongst the thickest and most symmetrical of these 

 is our A. coronata (Ann. Nat. Hist. ser. 3. vol. xix. p. 294, pi. 10. 

 figs. 15, 16) ; whilst the thinnest and most outspread is the A. 

 Rotula, D'Orb. (For. Foss. Vien. pi. 10. figs. 10-12). This last- 

 named variety, elegant in its delicate symmetry, is subject, 

 among other modifications, to a variable exogenous overgrowth 

 on its septal lines, as, for instance, Rosalina Edwardsiana, D'Orb. 

 For. Cuba, pi. 6. figs. 8-10, and Truncatulina ornata, D'Orb. 

 For. de I'Amer. Merid. pi. 6, figs. 7-9; and thus it insensibly 

 loses itself in the subsymmetrical and strongly limbate Planulina 

 Ariminensis, D'Orb. (Ann. Sc. Nat. vol. vii. p. 280, pi. 5. figs. 1-3, 

 Modeles, No. 49.) In our already quoted paper on the Rhizo- 

 pods of the Norway coast, we have erroneously placed PL Ari- 

 minensis among the synonyms of Operculina complanata, misled 

 by its extreme similarity of shape. 



Soldani has devoted many plates in his ' Testaceographia ' to 



* In his genus Planorhulina, D'Orbigny placed also some Spirilline 

 varieties of Kotalia repanda (such as PI. vermiculata). 



