1 78 Messrs. W. K. Parker and T. R. Jones on the 



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

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

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

 the little so-called Rosalines, Rotalince, Anomalina, and Planu- 

 lince, are equally simple dwarf forms ; their relative vesicularity 

 or 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. lobatula, 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. Planorbulina 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 vulgaris, 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 Acervulina by Schultze. Arrested con- 

 ditions of this biconvex variety constitute the Anomalince of 

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

 is our A. coronata (Ann. Nat. Hist. ser. 2. 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 PAmer. 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. 13, 

 Modeles, No. 49.) In our already quoted paper on the B/hizo- 

 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 Planorbulina, D'Orbigny placed also some Spirilline 

 varieties of Rotalia repanda (such as PL vermiculata). 



