- 736 MR. P. H. CARPENTER ON THE [Dec. 19, 
division of 3 joints, the axillary with a syzygy. Subse- 
quent divisions of two joints united by syzygy. 
nove-guinee. 1(2)A’RDPP. 
typica. 1A'RDS. 
B. Second and third radials united by ligament. 
Many arms. First ray-division of three joints, the axillary 
with a syzygy- 
a. Rays divide three times. Subsequent divisions like the first. 
robustipinna. A'(D)P=". 
japonica. 3A'Re- 
parvicirra. 3A'DP®, 
8. Rays may divide five times or more. 
I. Third and fifth ray-divisions like the first. Second and 
fourth divisions of two joints, the axillary without a syzygy. 
alternans. 3A'RPP’?. 
II. All ray-divisions like the first. 
schlegeli. 3A'RDP@. 
bennetti. 3A'RDPr. 
peroni. 3A’RDP?. 
Prof. Bell’s formule do not give any thing like a proper idea of 
the characters of Act. nove-guinee and Act. typica, especially the 
latter. Both species are among “those rare cases in which 
divisions extend beyond the palmars;”’ and Prof. Bell should there- 
fore have made use of his symbols P’ and P”. These two would 
have sufficed for A. nove-guinee, which has only two axillaries be- 
yond the palmars. Strictly speaking, however, neither P, P’, nor 
P” have any proper place in the formula; for the palmar and sub- 
sequent axillaries are not syzygial joints homologous with the dis- 
tichal axillaries, any more than the radial axillary is, either in these 
two species or in the solaris group ; and as pointed out above, it is 
equally incorrect, for morphological reasons, to describe the first 
brachials as being syzygial joints homologous with the third brachials 
1 Tt is absurd to put the D within brackets in this formula, because the only 
specimen described has no syzygy in the axillaries of three out of the nine 
primary arms. I have described a specimen of Ac?. parvicirra in which five 
out of the ten distichal axillaries have no syzygy, and another in which there 
are four axillaries with and four without a syzygy. Here therefore we have a 
character which “ frequently though not always obtains” just as in Act. robusti- 
pinna. Why is the one case noted in the formula but not the other? Prof. 
Bell’s experience of the variations in these characters must surely have taught 
him that it is the exception and not the rule for all the distichal and palmar 
series of any many-armed specimen to be exactly alike, and that a specific dia- 
gnosis must be based on the characters of the majority. When, however, some 
specimens of any type have distichals or palmars, and others may be altogether 
without them it is useful to put the D or P within brackets; and this should 
have been done in Bell’s formula for Act. parvictrra, as I shall shortly point out, 
