1882.] CLASSIFICATION OF THE COMATUL/E. 741 



briareus (3A.Vl^ have the same formula, except as regarfls the 

 number of joints in the cirri ; but, for all I know, the one may have 

 20 arms only and the other 40, 60, or more. Act. multifida is a 

 many-armed form of this kind, having two joints in the palmar and 

 subsequent ray-divisions. Miiller describes the number of arms as 

 40-44, and I have seen individuals with even more ; but Prof. Bell 

 gives the species-formula as 3 A'D^, exactly the same as that of 

 Act. trichoptera, which has no palmars and 20 arms or less ! 



I cannot imagine what has led Prof. Bell to suppose that the 

 radial axillary of Act. multiradiata " is a syzygy," so that he has 

 inserted an R into his formula. Miiller made no mention of it in 

 his description of the type, as he did in the case of Act. Solaris and 

 its allies ; and in a memoir ' now three years old, after personally 

 examining the type specimens at Paris, I placed the species in a 

 group distinguished as follows — " Second and third radials united 

 by ligament only." Surely Prof. Bell has not understood Miiller's 

 expression, " Die axillaria der Arme mit Syzygien," to include the 

 radial axillary also^. With this R omitted and a missing (P') in- 

 serted, the formula becomes 2 A'DP(P')^ ; but it gives no information 

 whatever respecting the number of joints in the distichal and palmar 

 series. When the distichal axillary " is a syzygy," it is either united 

 by syzygy to the preceding joint {Act. jukesi), or there are two joints 

 below it, so that it is really the third distichal. This rule is an in- 

 variable one ; but even supposing it to be known to the readers of 

 Prof. Bell's formulae, the same does not hold good with the palmars. 

 For the palmar axillary, which " is a syzygy," may be the third of its 

 series, as in Act. parvicirra and Act. hennetti, or the second, as in 

 Act. multiradiata; or, like the distichal axillary of Act.jukesi, it 

 is syzygially united to the preceding joint, as in Act. typica. Prof. 

 Bell's formula, however, gives no information about this, and the 

 special distinctive character of the multiradiata group is thus alto- 

 gether lost sight of, unless No. 5 of the following Rules be under- 

 stood as known ; but Prof. Bell is silent upon this point. 



The weakness of his method of formulation is partly due to the 

 following cause : — The same symbol (D or P) is used indifferently, 

 whether there are three or two joints, the axillary with a syzygy, or 

 two joints united by syzygy. I should say, however, that the figure 

 indicating the position of the first brachial syzygy would in most 

 cases explain to an experienced worker which type was meant, as 

 is shown in the general rules stated below ; but Prof. Bell gives no 

 hint of this. 



The formula 3DP, which he gives for Act. parvicirra, would thus 

 admit of any of the nine following explanations, the third brachial 

 being a syzygy in all cases, and the two outer radials united by 

 ligament. In the other two columns are recorded some existing 

 species, the distichal and palmar axillaries of which are syzygies, 



1 Trans. Linn. Soc. 2ud ser., Zool. vol. ii. p. 27. 

 ^ The italics are mine. 



