REPORT ON THE CRINOIDEA. 401 



a stemless Urchin and a highly specialised Palseocrinoid, 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 " Ic dos des Astdries 

 correspondrait a la region buccale des Oursins et non a leur region anale," which not 

 even Ludwig would assert. Two years ago Perrier described a small Starfish which 

 had been dredged l)y the " Travailleur," and was distinguished by the possession of 

 a small dorsal a])pendage comparable to the stem of a Crinoid.^ He stated that 

 " quelques caracteres des Asteries dont nous avons k parler ici paraisseut indiquer 

 que I'appendice dorsal dont elles sont munies est bien reellement I'homologue du 

 pedoncule des Crinoides." He named the type Caulaster, and added that it is allied to 

 CtenodisGUS. " II existe chez ces derniers un leger tubercule qui nous paralt homologue 

 de I'appendice dorsal des Caulaster, et peut-^tre en pourrait-on rapprocher un boutou 

 saillant qui, chez les Agtropecten, occupe la j)lace oh se trouve I'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 Astropectinidae.^ It is " frequently developed 

 into an elongate tubular prolongation " in the subfamily Porcellanasteridse. He doubted 

 the affinity of Caulaster with Ctenodiscus, and was inchned to regard it as a young 

 Porcellanaster. More recently Danielssen and Koren ^ have described a new genus 

 Ilyaster, in which a disk of 30 mm. diameter bears an epiproctal process 8 mm. long 

 and covered with paxilte, as in the Astropectinidae described by Sladen. They agree 

 with Perrier in regarding it as homolooous 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 Astropectinidae would throw much light 

 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 I'appendice dorsal, se trouvent en efi'et quatre grandes 

 plaques calcaires, disposees en croix et portant chacune un petit piquant ; ces plaques 

 sont t, peu pres orientees dans la direction des hras ; une cinquieme plaque, alterne 

 avec deux d'entre elles et opposee a la plaque madreporique, fait evidemment partie du 

 meme cycle ; cinq autres plaques plus petites viennent se placer dans les angles laissds 

 libres par les cinq plaques de la premiere rangee. On ne pent manquer d'etre frappe 



^ Comptes rendus, t. xcv. p. 1379. = Journ. Linn. Soc. Land. (Zool.),vol. xvii. p. 214. 



' Den Norske Nordliavs-Expeditioii, xi.; Zoologie. Asteroidea, p. 101, pi. vii. lig. 16, 1884. 



4 Reports on the Results of Dredgins by the U.S. Coast Survey steamer -'Blake" ; Report on the Echini, Mem. 

 Mils. Comp. Zool, vol. x., 1883, No. 7, p. 17. 



(ZOOL. CHALL. EXP. —PART XXXII. 1884.) IlOl 



