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Show 738 MR. P. H. CARPENTER ON THE [Dec. 19, veniently described as consisting of distichal joints. But hi order to avoid misconception, I expressly inserted the word distichals in speaking of the first division of the rays of Act. pulchellal. The description of this species was written before those of the Leyden Comatula, and must have been read by Prof. Bell, as he gives a formula based upon it. I cannot help suspecting, however, from the formula which he gives for Act. altemans, that he has thus misunderstood m y meaning. It is as follows, 3ARPP"?. This can only be interpreted in the following way :-that the radial axillary " is a syzygy " (which is not the case) ; that there are two distichals2, the axillary without a syzygy (while there are really three, the axillary with a syzygy) ; that there are two or three palmars, the axillary with a syzygy (while there are really two, the axillary without a syzygy) ; and so on for the two remaining divisions, so that the formula should read 3 A'DP'P'"?. Even then, however, it would not indicate whether two or three distichals are present3, nor whether there are one or two palmars, nor the number of joints in the two remaining divisions ; so that one would be entirely at a loss as to the systematic position of the type. Prof. Bell gives the formula for Act. japonica as \/3 A'R £. Even after the removal of the unnecessary and totally misleading R, the formula is entirely incorrect as regards the ray-divisions, and says nothing about any palmars being present. It means that there are two distichals, the axillary not a syzygy. But in Miiller's classification this species is placed in a group distinguished as follows, " Die Axillaria der Arme mit Syzygien ;" and my own description runs, " Primary and secondary arms each of three joints, the axillary a syzygy," or, as Prof. Bell puts it, " Three distichals and three palmars, the axillaries syzygies." His formula should therefore be3A'DP|. The formula which he gives for Act. parvicirra (3A'DP - ) implies that palmars are always present on some of the rays. A specimen has been figured, however, with 13 arms only, having distichals on only three rays and no palmars at all; and others have been noticed with but 18 and 20 arms 4. The P should therefore be put within brackets, and the formula stand 3 A'D(P) (--, like that of Act. wahlbergi, Miill., and Act. variabilis, Bell, M S . In like manner the formula given for Act. peroni (^3A'RDP j^) does not convey the information that there may be another axillary 1 Bull. Mus. Comp. Zool. vol. ix. no. 4, p. 10. %1 I a m at a loss to understand how Prof. Bell can have supposed that the second joint after the radial axillary, which is described as bearing a pinnule, can at the same time be an axillary joint; but no other types without a syzygy in the axillary than a series of two distichals have yet been described. 3 I. e. unless the rule be known that if the distichal axillary is a syzygy it is always the third joint, and not the second, as may sometimes be the'case with the palmars. 4 Trans. Linn. Soc. 2nd series, Zool. vol. ii. 1879, p. 44, and pl. ii. fig. 9. |