﻿326 



INFERIOR OOLITE AMMONITES. 



regard this example — if confirmed by others — as distinct from the typical modesta- 

 forms, which do not show any feature like this at this size. But there are signs 

 of injury to the ventral area of this example — a slight displacement of carina ; 

 and it seems to me, upon the present evidence, that this specimen is an example 

 of modesta which has become thus remarkably costate owing to injury — in fact, 

 a pathological case of accelerated development. 



The type form («) of modesta agrees exactly in general outline with this 

 example, and only differs from it in having, throughout life, very small, rather 

 closely-set ribs, which show only a slight tendency to become more distant with 

 age. The bend of the umbilicus is, in all respects, similar to that of the example 

 depicted. 



There is another form (/3) which I have classed under the same specific name 

 for the sake of convenience. It is more umbilicate, and is certainly smoother — in 

 fact, it appears almost destitute of ornament, except just in the central whorls, 

 and except for a few irregularly-placed obscure ribs on the outer whorls. 



It is obviously a development of the umbilicate form of dominans, 1 which I 

 have no doubt could be traced back to some more umbilicate and less costate form 

 of mar ginata, so that it would really belong to a distinct genetic series. The type- 

 form is probably descended from dominans a, but there is a considerable distance 

 between it and that form. 



Bonn, modesta is a common species in the Concavum-zone of Bradford Abbas. 

 It may be recognised from any Sonninia. hitherto figured by the deficiency of 

 ornament ; and it illustrates in a remarkable manner the retrogression to which 

 the series has attained, the rudimentary umbilical spines being the only evidence 

 of the rrassis2rinata-iorms. In fig. 1, PI. LXVIII, is depicted an example which 

 is somewhat abnormal, so far as the last quarter-whorl is concerned, presumably 

 on account of injury. An outline of its front view is shown in fig. 2. In fig. 5 of 

 PI. LXX the suture-line of a normal modesta, a is delineated, illustrating the 

 tendency in the broader-whorled forms to unduly elaborate the outer lobule of 

 the superior lateral lobe. 



Sonninia simplex, 8. Buckman. Plate LXX, figs. 2 — 4. 



Discoidal, compressed, partly sub-carinate. Whorls oblong in section, marked 

 only with very fine, sub-direct, ventrally-inclined growth-lines. 2 Ventral area 

 convex, divided, only during immaturity, by a very rudimentary carina about the 

 size of a pencilled line. At early maturity the ventral area (when the test is 



1 I could figure all the gradations between dominans /3 and modesta ft (see p. 324). 



2 On the core of the body-chamber are some irregular bulgings due to irregularity in thickness of 

 test. They make no impression on the outside of the test. 



