16 GEOLOGICAL MEMOIRS. 



On the Arms of Cystidea. By Dr. Alex, von Volborth. 



[This article is the translation of an introductory chapter to a memoir on the 

 Russian Sphaeronites, published in the Transactions of the Mineralogical Society 

 of St. Petersburg for the year 1845-6, and also printed in a separate form as a 

 pamphlet : the memoir contains a systematic account of all the Russian Sphaero- 

 nites hitherto known, a list of which is appended to the present translation. — Ed.] 



The Sphaeronites form a distinct subdivision of the so-called arm- 

 less Crinoida which have been recently brought together under the 

 name of Cystidea*, and although I do not agree with the definition 

 of this group as set forth by M. von Buch, I am willing to retain the 

 name, provided it is not understood as involving the idea of the 

 absence of arms. M. von Buch however absolutely denies the exist- 

 ence of arms in all the Cystidea, and speaks of the articulated 

 organs of the Echino-encrinites, described and figured by me in 

 1844't as tentacula % (Armtentakeln oder Fiihlertentakel). Now it 

 is true that the soft tubular and contractile organs covered with 

 skin and having the upper and under side alike, such as those which 

 surround the mouth in many Echinoderms and Polyps, have been 

 called indifferently tentacula and arms, because they not only serve 

 as organs of touch, but by means of special contrivances, stinging, 

 hooking and clasping, they really perform the part of arms. I am 

 not however aware that the articulated hard crinoidal arms with 

 distinct dorsal and ventral sides have ever been called tentacles, al- 

 though they are certainly not without the sense of touch. 



The reasons for assuming the absence of arms in the Cystidea 

 seem to be the following : — 



1st, Because they have only been found once. Even however 

 supposing that the arms had only been met with in one instance, 

 M'hich by the way is not the case, since I have myself described and 

 figured them in two species of Echino-encrinites, one cannot imagine 

 why a fact is to be denied because there is only a single instance 

 of it. 



2ndly, Because the arms are not similarly placed to those in true 

 Crinoidea. The arms are articulated, have a ventral groove covered 

 with tentacles, and proceed from the dorsal portion of the cuticular 

 skeleton — clear essential characters of crinoidal arms ; their position 

 nearer the mouth cannot deprive them of this designation, and only 

 affords an additional reason for arranging these animals in a group 

 distinct from the Crinoidea. The arms of the true Crinoidea are no 

 doubt inserted in a very different manner. 



Lastly, The Cystidea have a special ovarial orifice on the cup, 

 and therefore do not require arms connected with the organs of re- 

 production, which in existing Crinoids are always to be recognized, 



* See Quart. Geol. Journ. vol. ii. part 2. p. 20. 



i Bullet, de la ClassePhys. Math.de I'Acad. Imp. des Sc. de St.Petersb. 1845, 

 t. iii. p. 91. 



X The arms of the Echino-encrinite are furnished with tentacula on the ventral 

 side. What is meant by * Fiihlertentakel,' I do not understand ; perhaps ten- 

 tacles of a higher order intermediate between arms and tentacles ? (See Transl. 

 I. c. p. 37..) 



