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Show •J CLASSIFICATION OF THE COMATULA 741 briareus (3AH^j have the same formula, except as regards 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. multiflda 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 Muller's expression, " Die axillaria der Arme mit Syzygien," to include the radial axillary also2. With this R omitted and a missing (P') inserted, 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 invariable one; but even supposing it to be known to the readers of Prof. Bell's formulas, 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. bennetti, 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 altogether lost sight of, unless No. 5 of the following Rules be understood 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. 2nd ser., Zool. vol. ii. p. 27. 2 The italics are mine. |
