GENUS NUMMULINA. 271 



divided by prolongations of the marginal septa. These prolongations, in several of the 

 smaller Nummulites (for the most part belonging to the group of Flicata vel striata of 

 MM. D'Archiac and Hainie), converge radlalli/ towards the centre, sometimes with a slight 

 sinuosity. In a considerable proportion, however, of the middle-sized and larger Nummulites 

 (including the whole of the Laves and sublaves, and several of the Piuictulatce, of MM. 

 D'Archiac and Haime), the septal prolongations, though commencing radially at the 

 margin, as shown in Plate XVIII, fig. 1, />,' h' , soon become more or less sinuous, and meander 

 without any definite direction over the whole surface of the disk, occasionally bifurcating 

 near their origin, as shown at h" , b" . Another variety in the disposition of these alar prolonga- 

 tions of the septa consists in the formation of inosculations between those which adjoin one 

 another, so that the extensions of the chambers over the lateral surfaces are divided-up 

 into numerous isolated portions, as shown in fig. 9 ; and it is this arrangement which gives 

 rise to those numerous interruptions in the interspaces between the successive whorls, which 

 mark such vertical sections as the one represented in fig. 10. Further, these inosculations 

 may be so frequent as to convert the whole system of septal prolongations into a reticulation 

 covering the invested whorl, as shown at U , L', fig. 3 ; in which reticulation the continuity of 

 those prolongations is altogether lost. The Nummulites in which this plan prevails are 

 distinguished by MM. D'Archiac and Haime as Reiicidata and Sabreficulalce. Thus, as has 

 been pointed out by Messrs. Parker and Rupert Jones (lxxx /j), there are three typical plans 

 on which these alar prolongations are arranged, namely, the radiate, the sinuate, and the 

 reticulate ; but the first of these graduates imperceptibly into the second, and the second, 

 with the like absence of any definite boundary, into the third. Among the I'cputed species of 

 Nummulina, there are some {N. striata and N. Biaritxensis, for example) of which some indi- 

 viduals have radiate and others sinuo-radiate septal prolongations ; whilst there are several 

 (especially among the medium-sized '•' granulate" forms) which are radiate in their young 

 state and sinuate when older. The passage from the sinuate to the reticulate plan, 

 moreover, is marked by varieties of N. eomphmata, wherein inosculations of the septal 

 prolongations occur which assimilate their arrangement to that presented by varieties of 

 some of the sub-reticulate forms, as N. Immgata, which depart but little from the sinuate 

 type. 



463. In all the larger forms of typical Nummulites we find columns of non-tubular 

 substance based upon the septal bands of tlie interior convolutions, and recdving additions 

 to their height from successive investments of the spiral lamina, the substance of which is 

 tubular where it overlies a surface whose tubularity allows the exit of pseudopodia, whilst it 

 is non-tubular when the subjacent surface is of the like description. In N. loevigata and 

 several other Nummulites, we see these columns (the form of which is very irregular) to be 

 included between the two lamellae of the alar prolongations of the septa, which diverge to 

 give them passage, as shown at e,' e , e', fig. 9. In other instances, however, these columns 

 pass up through the intermediate portions of the chambers, as is the case in N. Garansensis 

 (fig. 3), but still more remarkably in N. Vernettili (see i, plate vii, fig. 1 d) and N. Leymeriei 

 (i, plate xi, fig. 10 e). It is certainly the exception rather than the rule to be able to trace 

 these columns from the inner convolutions to the surface with the continuity shown in 



