OCR Text |
Show 1882.] CLASSIFICATION OF THE COMATULCE. 739 beyond the palmars. It should read 3 A'DP(P') £. There may be yet another in Act. bennetti and the number of arms reach 70 or 80, which is only very rarely the case among the Comatula. Prof. Bell's formula (3 A ' R D P £), however, only provides for 40, which is a very common condition. The formula should therefore be 3 A DPP'(P") ?. The same may be said of Act. schlegeli, the only known example of which has two axillaries beyond the palmars and over 80 arms. Its proper formula would be 3 A'DPP'P" ~} while Prof. Bell gives 3 A ' R D P f, which provides for less than half this number of arms, so that one of the most evident specific characters is not taken into account at all. The ray-divisions of Act. pulchella have been thus described:- "}?720 a.r™s> most of tne rays usually dividing twice, the first division (distichals) consisting of two joints which are not united by syzygy- When the arms spring directly from the radial axillary, the two lowest brachials are united by ligament, as in most Comatula, and the third is a syzygial or double joint. But in all the arms which spring from a distichal axillary the two lowest brachials are united by syzygy to form a double joint; and the true third brachial, which is also a syzygial joint, as in all Comatula, thus becomes the second arm-joint, as in Act. Solaris"1. Two formulae are necessary for this type-one for the ten-armed form, and another for that with divided primary arms. The first would be 3 A'g, and the second Vl.2A|. Prof. Bell, however, writes (1.2)3 A5, thus taking no account of the presence of distichal axillaries in some (often all) of the primary arms ; and his formula also implies that the first, second, and third brachials of the same arm may all be syzygial joints, which is never the case. One very serious objection to Prof. Bell's system of shorthand is that (except in one case) it is only applicable to those Comatula in which the ray-divisions are regular, i. e. with the second and subsequent divisions all resembling the first. For regular forms like Act. parvicirra, Act. bennetti, and their allies, which have three distichals and three palmars with a syzygy in each axillary, Prof. Bell's notation is probably as short a one as could be devised ; though it gives no information respecting the number of joints in each series, and does not always indicate whether palmars are present or not. Thus, for example, his formula for Ant. articulata is \3 A~. This means that distichals are present hut do not " present a sygygial joint." It does not indicate, however, whether the axillary is the fourth joint (an actual case in another species), the first (which I have never met with), or the third, or the second (as is really the case). But no information is given at all respecting the presence or ' Bull. Mus. Comp. Zool. vol. ix. no. 4, p. 10. October 1881. Were I writing now, I should insert the word "nearly" before "all Comattdm" in the last sentence. |