1882.] CLASSIFICATION OF THE COMATULiE. 743 



The want of elasticity which renders Prof. Bell's system so mis- 

 leading will not he found, I hope, in that which I am now about to 

 explain. It has grown up gradually during seven years' work, and 

 will meet all the variations of actual Comatida-structare with which 

 I am acquainted, together with any others that I can imagine as 

 possible. Some time ago I pointed out that " the first and second 

 segments beyond every axillary, whether radial or brachial, are 

 nearly always united together in the same manner as the second and 

 third (axillary) radials." Further experience has shown that the 

 " nearly " embraces several well-marked but regular exceptions to 

 the above statement ; and I have therefore drawn up the following 

 rules, which embody the results of my study of the group. They 

 are not to be in any way regarded as laws of (7o»2«^M/a-structure, 

 but merely as generalizations based upon a knowledge of some 

 400 species, and therefore, I hope, of some value for the purpose of 

 classification, 



1. All ten-armed species of Actinometra which have the two 

 outer radials united by syzygy, have the first two brachials united 

 in the same way. 



Ex. Act, Solaris. No Antedon known. 



2. All many-armed species of Actinometra which have the outer 

 radials united by syzygy either have (a) all the ray-divisions of two 

 joints also united by syzygy and the first two brachials similarly 

 united ; or (/3) there may be three distichals, of which the first two 

 are articulated and the axillary is a syzygy, while the subsequent 

 divisions are as above. 



Ex. a. Act.jukesi; j3. Act. typica. 



3. If the two outer radials are united by a ligamentous articu- 

 tion, the next two joints are similarly united, whether there be ten 

 or many arm?. In the former case the third brachial is almost 

 always a syzygy. (One of the " Blake" Comatulce is an exception.) 



Ex. Ant. rosacea, Ant. philiberti. Act. meridionalis. Act. 

 parvicirra. 



4. In by far the greater number of Comatulce which have the 

 two outer radials articulated by ligaments and only two ray-divisions, 

 the third brachial is the lowest syzygial joint on the arms, whether 

 the distichal axillary be a syzygy or not ; and the two lowest 

 brachials are articulated by ligaments. 



Ex. Ant. macronema, Ant. rexjnaudi. Act. trichoptera. 



Exceptions. Act . jimbriata and Act. horneensis, with some unde- 

 scribed Antedon-%\>tcv^%, have the second brachial a syzygy, like the 

 distichal axillary. Act. pulchella and a new ' Challenger ' Antedon 

 have two distichals the axillary not a syzygy, but the first two 

 brachials united by syzygy. 



5. If the two outer radials are articulated and there are more than 

 two ray-divisions, so that palmars are present, the third brachial is 

 the first arm-syzygy in all cases but the following : — 



o. Two palmars united by syzygy ; the first two joints beyond 

 the palmar and all subsequent axillaries are also united by 

 syzygy. 



