FORAMINIFERA. 



349 



Figs. 17-20. FORAMINI- 

 I-EKAL SHELLS. (After 

 d'Orbignj.) 



17, Boterostciyiia dopressa ; 18, 

 Arapbigteglna Icwonii; 19. 

 Fabulnria digcolithus, mic of 

 the.Vio(Wre; ai, ()rl>iculina 

 numismalig, var. adimca. 



but differing from the last both as to its aperture and its segniental plan, also becomes sandy in old 

 age. The last three kinds are known both recent and fossil. 



The truly hyaline Foraminifera, with very small perforations of shell, have the one-chambered 

 Layena (flask) for their simplest type. This is often most exquisitely 

 delicate and elegant. In Glandulina (acorn-like, Figs. 21, 22) and Xodosaria 17 

 (knotty, Figs. 16 6 , 23. 24) we see a series of chambers planned on the 

 growth of successive Lagence, the base of the new one partly enveloping the 

 front of the last segment. The ornaments are various, but chiefly thin ribs 

 and delicate points. If not circular in section, but flat, the same kind of 

 growth produces Linyulina (tongue) and Frotidicularia (leaf, Fig. 16j). 

 If round in section, but bent, it is Dentalina (tooth, Fig. 1G 7 ). Still 

 further curved, whether thick or thin, convex or flat, smooth or ornamented, 

 this kind of Foraminifer becomes a Vayinulina (sheath), a Marginulina 

 (margin), and in the extreme a Cristellaria (crest, Fig. 16 S ). If the 

 segments grow alternate, we have either Polymorphina (many-shape) 

 or Uviyerina (grape-bearer, Fig. 33). The last is not so common as the 

 others of the Lagenidte, which abound both recent and fossil. Another 

 set of hyaline Foraminifera has coarser pseudopodial passages through 



the shell, and more globular chambers, and these are set on in a somewhat heaped fashion, and but 

 roughly spiral, so that in most cases the stolon-hole of each chamber comes near to the other 

 apertures, and they all open into a kind of vestibule in the middle of the shell. These are the 



Globigerinat (globe-bearer, Fig. 16 9 ). Some abound in the 

 Chalk, while others are met with in the present seas and 

 oceans. They may all be said to be of the same species as 

 the common GL bidloides, figured and described by d'Orbigiiy. 

 The form most common in the Chalk (Gl. cretacea) is the 

 most truly spiral of all the varieties. The Adriatic yields 

 a neat Gl. bulloides, which is also met with at many places in 

 the great seas ; and it lives and thrives in the abyssal depths of 

 the ocean, attaining a relatively large size, and putting on coarse 

 prickles and a much thicker shell than it has in shallow waters. 

 On the surface of the ocean another variety is found floating j 

 it is like bnJloides, but with enormously long, hair-like prickles ; these in life are invested with 

 sarcode, which, on the outside, becomes coated with shell in Orbulina (globe). 



The Rotalia (wheel, Figs. 16 10 , 34) is a type, or leading form, among an immense series 

 of more or less spiral Foraminifers, varying in their shell-structure plan of spire from nearly top- 

 shaped to flat (with occasional loss of spire in either a cylindrical or a heaped growth), and the shape 

 and position of aperture. Pidvimdina (cushion), Discorbina 

 (basket 1) Planorbulina (flat-circle, Fig. 29), and Ccdcarina (spur, 

 Fig. 31), are other important members of the Rotaline group. 



Under the heading Nummulitidce are grouped some high-class 

 Foraminifera, which, however, have their simple types among 

 them and closely associated. Thus the little, thin, neat Nonionina 

 (from " nonion," a fancy name) leads up, by more and more complex 

 shell- structure, to Polystomella (many-mouth) ; and the relatively 

 simple Operculina (like the opercidiun of some gasteropods) is at 

 the root not only of the greater and complex Nummulites (coin- 

 like), but also of its congeners on one hand, Amphistegina (double- 

 stage, Fig. 18), and, on the other, the more cyclical Heterosteyina 



(odd-stage, Fig. 17), with Cycloclypeus (circle-shield) and Orbitoides (circle-like). Most of the 

 Nummulitids, except Orbitoides, occur abundantly in some sea or other. Nummidites is not rare, 

 though small, in the Australian seas ; but in the fossil state it constitutes masses of limestone, 

 hundreds of feet thick, and hundreds of square miles in extent. Of these limestones many great 



FigS. 21-24. FORAMINIFERAL SHELLS 



(Afar d'Orbigny), FIGURED WITH THE 



APERTUKE DOWNWARDS. 



21, 22, Glmidiilinn laevifrata, outside and section ; 

 23, 24, Nodoaaria lamcllosa, outside and scot ion. 



FigS. 25-28. F 3 R A MINI f E 11 AL 

 SHELLS (After d'Orligny), FIGURED 

 WITH THE APERTURE DOWNWARDS. 



25, 26, Testularia nciculata, outside and 

 section; 27, 28, Bigenerina (Trxtulana) 

 nodosaria, outside and section. 



