SONNINIA SIMPLEX. 423 



The abnormal form has septa which are similar, but they are much less 

 elaborate in outline, and lack the bipartition of the outer lobule ; in fact, the lobe- 

 line appears to have undergone degeneration, though of course it may never have 

 attained to the elaboration of type modesta. More evidence is required on this 

 head before it can be decided whether the forms are properly united under one 

 name. Barring the coarse ribs of the " abnormal " form, the only external differ- 

 ence is its greater smoothness. 



Of the form alluded to as modesta /3 (p. 326), an example sufficiently satisfac- 

 tory to give a good figure with its septation has not yet been worked out. 



In PI. XCV, fig. 3 shows the side view of the type of this species reduced to 

 one-half natural size, fig 4 the front view in outline similarly reduced, and fig. 5 

 the suture-line. A young typical specimen illustrating the spinous stage followed 

 by the subcostate stage is depicted in PI. XCVI, fig. 1, view of part of its 

 periphery fig. 2, both these figures being of natural size. 



Sonninia simplex, S. Buchiian. Plate CIII, fig. 11. 



See Plate LXX, figs. 2, 3 (not 4), and page 326. 



For the description given of the suture-line substitute the following : 

 suture-line somewhat degenerate, denticulation being weak, L markedly asymme- 

 trical, the terminal lobule very intra-axial, anisosceloid, inequicellate, the lateral 

 lobules markedly anisometric, the inner aborted, the outer tripartite. 



From gibbera to simplex is a very long jump, but the septa of the type which 

 have now been worked out suggest this association ; there is the same abortion of the 

 inner lateral lobule of L, and even a similarly curved terminal lobule. In outline 

 the septa would appear to have undergone phylogenetic degeneration, for the 

 denticulations are not sharply and deeply cut — compared with those of modesta 

 (PI. XCV, fig. 5) there is a marked contrast ; but there is a certain similarity to 

 those of the "abnormal" modesta. The latter, however, has a more developed 

 inner lobule of L, and a less markedly bipartite outer lobule. The interposition 

 of modesta between gibbera and simplex lessens the gap between these forms, but it 

 seems to make the decline in the septation of simplex all the more marked. 



In PI. LXX, fig. 4 shows a suture-line taken from a specimen externally 

 similar to the type simplex. Yet its suture-line differs because it shows L without an 

 aborted inner lobule. It would, therefore, seem that similar as this specimen is, it 

 has been the offspring of another genetic series, which did not abbreviate the 

 inner lobule in catagenesis (see the subirregidaris-series, Sonn. subsimplex, p. 427). 



