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Show 744 MR. P. H. CARPENTER ON THE [Dec. 19, Ex. Species B. of above scheme. /3. Two palmars, the axillary a syzygy ; the second joints beyond the palmar and all subsequent axillaries also have a syzygy- Ex. Act. multiradiata. Species A of the above scheme, with the first two brachials united by syzygy, is an exception. 6. Whenever any ray-division, distichal, palmar, or any other, consists of three joints, the first two are articulated by ligaments, the second bearing a pinnule, and the third (axillary) is a syzygy just as in the first three brachials of Ant. rosacea and Act. echino-ptera. When, however, there are only two joints, and the second (axillary) is a syzygy, the first has a pinnule, just as in the arm-bases of Act. fimbriata. 7. The hypozygal of a syzygy is always united to the preceding joint by a muscular articulation. Like Prof. Bell, I should use R to denote the syzygial union of the two outer radials. When ten arms only are present, this is indicated by 10 in the formula. This may be thought unnecessary, as the absence of any signs for the distichals would indicate that the primary arms remained undivided ; but I find that it is more convenient to indicate this character, which is generally a sharply defined one, in a positive rather than in a negative manner. I also assume, in accordance with Rules 3-5, that the first syzygy on the arm is on the third brachial, unless otherwise stated. If it is on the second brachial, I put 2 b at the end of the formula; and if the first two brachials are united by syzygy, % is used. In like manner, and in accordance with Rule 5, 2 d and 2 p would indicate that there are two distichals or two palmars, of which the axillary is a syzygy ; and g or | that the two distichal or palmar joints are united by syzygy- The figures 1 or 2 alone would indicate that there is either only a single axillary joint, or two which are united by ligament; and a 3 would denote three joints, of which the axillary is a syzygy l. If one figure occurs alone in a formula, it indicates the presence of distichals only; two figures, that palmars occur as well; and so on, an additional figure being added for each ray-division, e. g. Act-altemans 3,2,3,2. This may be tabulated as follows :- Symbol used. Character. Distichal. Palmar. One axillary joint 1 1. Two joints united by syzygy |. Two articulated joints 2 2. 1 It would, of course, be more consistent to write 3 d, or 3 p; but the syzygial nature of the third_(axillary) joint is such a constant character (Rule 6) that, until an exception is met with, I prefer to use the figure alone, for the sake of brevity. |
