132 THE VOYAGE OF H.M.S. CHALLENGER. 
form which they have described so ably under the name of Ilyaster mirabilis supports 
the views upheld by Perrier, and should be ranked in the same category as forming “a 
connecting link between Crinoidea and Asteroidea” on account of the presence of its 
remarkably developed dorsal appendage. 
It is probable that the apical plates of I7yaster have never yet been observed (they 
had not been seen when the type, which is probably too large to possess them, was 
described) ; and I venture to consider that the abactinal prolongation in J/yaster, like that 
in Caulaster, is also an anal funnel (whether functional or not I cannot say), and that, 
such being the case, it does not lend any support to the view that this remarkable 
development is in any way homologous to the stem of a Crinoid. I would further remark 
that this most interesting form Ilyaster mirabilis appears to me to be more nearly allied 
to the Astropectinide than to any of the genera which I have included in the family 
Porcellanasteridee. 
With reference to the foregoing remarks, it may be pointed out that Dr P. Herbert 
Carpenter’ hesitates to accept the homology of the dorsal appendage of Caulaster and 
Tlyaster with the stem of a Crinoid, and considers that the assumption is not yet satis- 
factorily proved. Carpenter also points out that Perrier’s comparison of the plates round 
the dorsal appendage of Caulaster with those forming the periproct of an Urchin cannot 
be followed out in detail, as, according to Perrier’s description, the apical system of 
Caulaster consists, not of genitals and oculars (basals and radials) as in an Urchin, but of 
under-basals and basals. With these views I entirely concur. 
In conclusion I would add that I am altogether at a loss to reconcile Perrier’s view 
according to which “le dos des Astéries correspondrait & la région buccale des Oursins et 
non 4 leur région anale”* with his comparison of the apical system of Caulaster with that 
of an Urchin.’ For either the proposition is self-contradictory, or, if it be true that the 
abactinal area of Caulaster corresponds to the apical region of the Echinoid, whilst the 
abactinal area of all other Asterids corresponds to the buccal region, it seems to me only 
another way of saying that the abactinal area of Caulaster corresponds not to the 
abactinal area, but to the actinal area in other Asterids. I will not do M. Perrier the 
injustice of thinking for a moment that he believes this to be the case. 
For my own part I consider, along with Lovén,* Carpenter,’ Agassiz,° and other 
naturalists, that the buccal region of an Asterid, of an Echinoid, and of a Crinoid are cor- 
respondent, and consequently that the apical systems of an Asterid or Kchinoid. and the 
calyx of a Crinoid are homologous parts. . 
1 Report on the Crinoidea, Voyage of H.M.S. Challenger, Zool. Chall. Exp., 1884, Part xxxii, p. 401. 
2 Nouv. Archives Mus. His. Nat., 2e Sér., 1884, t. vi. p. 162. 3) 
3 Comptes rendus (Dec. 1882), t. xcv. p. 1380. 
4 Etudes sur les Echinoidées, K. Svensk. Vetensk. Akad. Handl., 1874, Bd. xi. No. 7. 
5 Report on the Crinoidea, Voyage of H.M.S. Challenger, Zool. Chall. Exp., 1884, Part xxxii. p. 401. 
6 Mem. Mus. Comp. Zool., Harvard, 1877, vol. v. No. 1. 
