Dr. J. E. Gray on the Genus Rhopalodina. 



301 



XXIX. — Description of Rhopalodina, a new form of Echinoder- 

 mata. By J. E. Gray, Ph.D., F.E.S., V.P.Z.S. &c. 



Among the specimens collected by the late Mr. Cranch during 

 Captain Tuckey's Congo Expedition, is the case of a very curious 

 animal which has been erroneously placed among the Worms. 

 By the label on the bottle it was taken on the " 22nd of May." 

 After examining the specimen I feel convinced that it is a 

 Radiated animal most nearly allied to Siphunculus, and probably 

 forms the type of a new family intermediate between that genus 

 and Holothuria. Unfortunately the whole of the internal organs 

 appear to be destroyed, either by the weakness of the spirit, or 

 their expulsion by the contraction of the organs at the time of 

 death ; for when the specimen was first examined, the sides of the 

 body were closely compressed against each other, leaving no in- 

 ternal cavity, and giving the specimen the form of a spoon with 

 a roundish bowl and a slender tapering blunt handle ; but when 

 carefully examined it showed that its proper form was ovate, 

 rather compressed, with a slight keel on each side. 

 It mjay be described thus: — 



Rhopalodina. • ' 

 Animal elongate, clavate, rigid, rather brittle, covered with 

 imbedded hard calcareous plates having the appearance of rugose 

 spinulose scales, the imbricate edge being directed towards the 

 aperture ; the scales of the dilated lower part of the body 

 large, and those on the narrow tubular part very small and close, 

 being most distinctly visible round the edge of the oral aperture. 

 When examined under the microscope the surface appears to be 

 formed of very numerous small circular imbedded plates, and 

 scattered with rather distant transparent rugulose spines. 



The upper part near the mouth is cy- 

 lindrical and tubular and more rigid, very 

 gradually and slightly enlarging towards 

 the end, where it rather suddenly dilates 

 into an ovate, somewhat compressed body, 

 with a slight keel on each of the two 

 edges. The parietes of the body are 

 thinner and less rigid than that of the 

 tube. The hinder half of the dilated body 

 is furnished with ten bands or ambu- 

 lacra, each formed of two series of thin 

 tentacles, supported or defended by trans- 

 parent rugulose spines, which regularly 

 diverge from the centre of the hinder 



Rhopalodina lageniformis. 



end of the body. They are more Uke the ambulacra of the 



