OCR Text |
Show 254 PROF. F. J. BELL ON THE GENUS AMPHICYCLUS. [May 6, There are no calcareous plates or spicules developed in the walls of the body or of the tube-feet, the only calcareous deposits being the terminal plates of the tube-feet, and the delicate and elegant bars which are found in the tentacles l. The integument is very thin anteriorly, but increases considerably in thickness in the hinder part of the body, where it is quite stout. When its walls were cut through, the anterior portion of the body-cavity was found to be filled with a large number of stout, rather short genital tubes, which branched only once or twice, but were so numerous as to obscure considerably the underlying parts. The retractors of the pharynx are inserted behind the middle point of the body; two of them are remarkable for approaching and uniting with one another ; under the band thus formed, on one side the intestine passes twice. The intestine is very delicate. No Polian vesicle was detected, and it is probably of comparatively small size ; the so-called water-lungs extend forwards to the anterior end of the body. The characters presented by this form are sufficiently remarkable to justify the establishment of a new genus for its reception. It stands nearest to the two genera instituted by Ludwig-Echino-cucumis and Actinocucumis • but it differs from them both in the important character of the regularly paired disposition of the radially placed smaller tentacles. With them, it differs from all other polychirote (or Dendrochirotae with more than ten tentacles), and agrees with the more simple of the decachirote Dendrochirotae in having the sucker-feet confined to the ambulacra. In consequence of the definite disposition of the tentacles in two cycles, I propose to speak of it as Amphicyclus, this form of the name being sufficiently different from Amphicyclia 2. The Generic Characters appear to be :-Stichopod arrangement of the suckers associated with the possession of more than ten oral tentacles ; the tentaclesjn two circles : those of the inner are arranged in pairs, are ten in number, radial in position, smaller than those of the outer circle, in which there are fourteen subequal tentacles. There are no calcareous pharyngeal plates, and two of the retractors of the pharynx are united with one another. As there is only one species known, the discrimination of the specific characters is, of course, unsafe ; but these appear to be :- (1) Complete absence of rods or spicules from the walls of the body or tube-feet ; (2) attenuation of the hinder end; (3) thinness of integument of anterior end ; (4) large number of genital tubes. As the locality is known (lat. 41° 12' N., long. 140° 45' E.; 43 fms., sand and mud), I propose the specific name of japonicus. The useful classification proposed by Professor Semper in his magnificent work has been universally adopted by systematists since the year 1868; in it the Dendrochirotous Pneumonophora were 1 In Cucumaria frondosa, where calcareous deposits are reduced to a minim u m , there are well-developed plates in the tentacles ; and Thyone okeni (see Brit. Mus. Cat. ' Alert' coll.) has rods in the tentacles only. 2 Haeckel, Jenaische Zeitschr. vol. xv. |