732 MR. p. H. CARPENTER ON THE [DeC. 19, 



applies it to denote the varying characters of the cirri ; and I shall 

 have much pleasure in employing it to this extent. His idea of dis- 

 tinguishing Antedon and Actinometra by A and A' respectively is 

 also a good one; though I should myself prefer A and a, as being 

 less liable to printers' errors. 



He gives formulje for 58 species, 1 2 of which are MS. names of 

 his own ; but of the remaining 46 formulae, no less than 12 would 

 lead a collector who depended upon them for identification of a speci- 

 men to form a false conception of the corresponding species. In 

 the case of Act. parvicirra and Act. novce guinece, the error is but a 

 slight one. But the formulae given for Act. bennetti, Act. peroni. 

 Act. schlegeli and other species denote a type of the genus which I 

 have never met with, much less described ; and were it not that I 

 am now prepared for nearly any freak of nature among these 

 animals, 1 should almost venture to call it a " Comatulid impossi- 

 bility." 



Eight of these twelve species (including the three above men- 

 tioned) have been described by myself in the ' Notes from the 

 Leyden Museum,' vol. iii. ; and as these Notes have a far less wide 

 circulation than the Proceedings of the Zoological Society, it is 

 necessary to prevent other workers from forming the wrong concep- 

 tions of these types which would result from the exclusive use of 

 Prof. Bell's formulae. 



The errors are in the parts of the formulae which denote the cha- 

 racters of the rays and their subdivisions, the remaining portions, 

 which indicate the positions of the syzygies in the arm-bases and the 

 characters of the cirri, requiring no alteration. As regards the for- 

 mer. Prof. Bell says: — 



"If (1) we use the letters i?, D, P for the radials, distichals, and 

 palmars respectively, and insert them in the formula whensoever the 

 respective axillary is a syzygy, we may (2) distinguish which of the 

 first three brachials (one of which is, with but with very rare excep- 

 tions, a syzygy) is a syzygy by simply making use of the number 1 , 2, 

 or 3. . . . When a character frequently, though not always, obtains, 

 the corresponding letter is put within brackets. . . . When D or P 

 appear in a formula it is clear the species must have more than 1 

 rays', because of the meaning of the words those letters represent ; 

 where, however, neither distichals nor palmars present a syzygial 

 joint, it will be necessary to make use of the mathematical sign for 

 the square root to mark the fact of its being a multiradiate species" 

 (pp. 531-532). 



' Prof. Bell has here confomifled the ten primary arms with the rays proper, 

 hy the division of which these arms originate. This has led him into much con- 

 fusion, as will be pointed out later. According to Miiller, " Kadien nenne ich 

 die auf dem Knopf aufgesetzten Stamme der Arme. . . . Auf jedem der 5 Kelch- 

 radien sitzen '2 Arme, die entweder einfach bleiben oder sich noch einmal oder 

 mehrraal wieder theilen." (" Ueber die Galtung Comahda, Lam., und ihre Arten," 

 Abhandl. d. Berlin. Akad. 1849, p. 240. j The arms therefore were clearly distin- 

 guished from the rays by Miiller ; and it is a pity that Prof. Bell has confounded 

 them, especially as in the genus Promachocrinns there actually are ten rays 

 springing directly from the centrodorsal. 



