SONNINIA— REVISION. 383 



must be placed as f -f- |— |- 2z. Another species, say b', has, when compared with 

 A, characters like this, f -f- | + 2z ; and a further species, c', has a formula 

 | + f + 4z. When, therefore, b and b' are compared together, it is found that 

 each has the same degree of spinosity, but that b' has twice the degree of 

 asymmetry of L which b has ; and when o is compared with b' it is found to have 

 the same degree of asymmetry of L, but coupled with half the degree of spinosity 

 and a less degree of gibbosity. If, then, x degree of spinosity be taken as the 

 starting-point, c must be said to have acquired its degree of asymmetry later than 

 b' in relation to the spinosity ; because b' had only got its spinosity reduced one- 

 half when it had acquired 2z degree of asymmetry of L, whereas c has got its 

 spinosity reduced one-fourth before it acquired 2z degree of asymmetry of L. It 

 is this consideration which has been the guiding principle of the following 

 classification. Although possessing the same degree of asymmetry of L, c and b' 

 would be ranged in different stocks, because it would be considered that c acquired 

 its asymmetry of L later than b'. In fact, these species would be arranged in this 

 manner to show what is taken to be their genealogy, having regard to such 

 characters : 



yf + f+3 f + i + 2s. 



« + ?/ + «< 



In order to facilitate as much as possible the study of the species of Goncavum- 

 zone Sonniniae, their classification is first given in a skeleton form. Further, 

 the skeleton outlines of the principal types of L have been inserted in this 

 classification so that the reader can see the character on which the scheme is 

 mainly based. The names of the species belonging to each subdivision are 

 placed in their order, and references to the pages where they are mentioned are 

 attached to them. The species which have been already described bear two 

 references — the earlier one relating to the previous description, the later one to 

 any additional note that has become necessary. New species bear only one 

 reference each, namely, the number of the page where they are described. By 

 such means the whole classification is brought into a small compass, readily 

 available to the reader for examination and comparison; it is also a suitable 

 introduction to the more detailed specific articles which follow. 



