Bemarl's on the Fwaminifera. . By Prof. T. Rupert Jones. 87 



is a Bentalina with excentric orifice.* In Figs. 3 and 4 it lias lost 

 more and more of its bilateral symmetry, becoming a Marginulina ; 

 and its curvature becomes extreme and discoid al in Fig. 5. Here 

 the newest chamber is still simple, but the older part of the shell 

 has received a crest or keel — essentially a single, medial riblet. 

 Returning to the bent form of Nodosaria, in Figs. 6, 7, and 8, we 

 have stronger, neater, and more compact Marginidinie ; the last 

 one with a crest. By the transverse lengthening and obliquity of 

 the chambers, with corresponding lateral compression, we are led to 

 Figs. 9, 10, and 11, which end in the flat form of elongated 

 Cristellaria, termed Planularia ; whose close relation to the 

 discoidal type is beautifully shown by Fig. 12. 



The coiling of early chambers (as in Fig, 7) is often succeeded, 

 not by linear, but by continued spiral growth {Cristellaria), leading 

 ultimately to Figs. 13, 14, 15, and 16, with their various conditions 

 of keel, hmbation, and umbones, and very changeable proportions 

 (and hence shape) of their chambers, see PL CXXIX., Figs. 18 

 and 19, besides the more orDamented forms. Fig. 17 is another 

 ultimate Cristellaria of the same breed; but Fig. 18 has still 

 an elongate shape, leading, on one hand, to the nearly discoidal, 

 but arrested, Fig. 19 ; and, on the other, to the very thick forms 

 (Figs, 20 and 21), which are known as Defrance's Saracenaria 

 Italica, 



Eelerring to Fig. 1, we lose its roundness in the flatter Fig. 22 

 (Lingidina). The chambers, beginning to overlap at the edges in 

 Fig. 23, become chevron-shaped in Fig. 24 {Frondicidaria). Even 

 in Fig. 23, however, the early chambers are not simply linear in 

 growth, and this, increased in Fig. 24 to a subspiral arrange- 

 ment, leads through many gradations in these flat shells to a 

 spiral system of early chambers, as seen in Figs. 25 and 26 ; and 

 this Planularian growth remains free, without the overriding or 

 saddle-like chambers, in Fig. 27, essentially the same as Fig, 10 

 and its allies, and, excepting its relative thinness, equivalent to 

 Fig. IS, &c. One of its ornamented colocal varieties is shown in 

 PI. CXXIX., Fig. 12. 



Plate CXXIX. exhibits some of the ornamented analogues of 

 the above-mentioned varietal forms of Nodosarina. Fig, 1 a is a 

 Nodosaria with characteristic ornamental ridges, but they end 

 abruptly on each chamber, forming little spikes. In Fig. 1 h several 

 small spines or prickles are produced on each ridge or riblet of the 

 chambers of a slightly bent (Dentaline) Nodosaria. 



In Figs. 2-6 the riblets are represented by granules on some 

 allied Marginulin{e.'\ In some individuals (as in fig. 1, pi, 6, of 

 Von Hantken's Monograph) they become gradually confined to the 



* If the sliell were flattened it would be a VaginuUna.. 



t Marginulina WcthercUii of the London Clay is the same form. 



