REPORT ON THE CRINOIDEA. 401 
a stemless Urchin and a highly specialised Paleeocrinoid, I think that most naturalists 
will be inclined to regard the mouth of an Urchin as representing that of a Crinoid, and 
not the point of attachment between the stem and the body. 
If this last view be correct, it follows, as Perrier points out, that ‘le dos des Astéries 
correspondrait & la region buccale des Oursins et non leur region anale,” which not 
even Ludwig would assert. Two years ago Perrier described a small Starfish which 
had been dredged by the “ Travailleur,” and was distinguished by the possession of 
a small dorsal appendage comparable to the stem of a Crinoid.'| He stated that 
“quelques caractéres des Astéries dont nous avons & parler ici paraissent indiquer 
que Tappendice dorsal dont elles sont munies est bien réellement homologue du 
pédoncule des Crinoides.” He named the type Caulaster, and added that it is allied to 
Ctenodiscus. “Tl existe chez ces derniers un léger tubercule qui nous parait homologue 
de Yappendice dorsal des Caulaster, et peut-étre en pourrait-on rapprocher un bouton 
saillant qui, chez les Astropecten, occupe la place ot se trouve anus chez les autres 
Etoiles de mer.” Sladen subsequently pointed out that a central epiproctal prominence 
of this kind is very general in the family Astropectinide.’ It is “frequently developed 
into an elongate tubular prolongation” in the subfamily Porcellanasteride. He doubted 
the affinity of Caulaster with Ctenodiscus, and was inclined to regard it as a young 
Porcellanaster. More recently Danielssen and Koren? have described a new genus 
Tlyaster, in which a disk of 30 mm, diameter bears an epiproctal process 8 mm. long 
and covered with paxille, as in the Astropectinidee described by Sladen. They agree 
with Perrier in regarding it as homologous with the stem of a Crinoid; and it would 
appear that Agassiz is of the same opinion.* It may be that this view of the case is the 
‘right one; but it could only be satisfactorily proved to be so by the demonstration that 
the cavity of the epiproctal prolongation is derived from the right vaso-peritoneal tube. 
For it is a diverticulum of this division of the primitive body-cavity of Comatula which 
extends backwards and has the joints of the larval stem developed in its walls. Future 
observations upon the early larval stages of the Astropectinides would throw much hight 
upon this question. Perrier’s Caulaster appears to be the youngest known form pos- 
sessing this curious appendage, and some of the plates of the primitive calycular system 
are still visible. “A la base de Yappendice dorsal, se trouvent en effet quatre grandes 
plaques calcaires, disposées en croix et portant chacune un petit piquant; ces plaques 
sont X peu pres orientées dans la direction des bras; wne cinquitme plaque, alterne 
avec deux d’entre elles et opposée & la plaque madréporique, fait évidemment partie du 
méme cycle; cing autres plaques plus petites viennent se placer dans les angles laissés 
libres par les cing plaques de la premiere rangée. On ne peut manquer Vétre frappé 
1 Comptes rendus, t. xev. p. 1379. 2 Journ. Linn. Soc. Lond. (Zool.), vol. xvii. p. 214. 
3 Den Norske Nordhays-Expedition, xi.; Zoologie. Asteroidea, p. 101, pl. vil. fig. 16, 1884. 
4 Reports on the Results of Dredging by the U.S. Coast Survey steamer “Blake” ; Report on the Echini, Mem. 
Mus. Comp. Zodl., vol. x., 1883, No. 7, p. 17. 
(zoOL. CHALL. EXP,—PART XxxiI.—1884,) hi dl 
