Prof. J. Miiller on the Structure of the Echinoderms. 245 



with the Crinoids, and at the same time of their peculiarities, the 

 exact analysis of their calyces and the exposition of their genera. 

 That they are not armless, as had hitherto been generally sup- 

 posed, was first observed by A. von Volborth, who discovered the 

 arms in Echino-encrinus angulosus and striatus, subsequently in 

 Echinospharites aurantiurriy where they proceed from the mouth. 

 The figures of the Duke of Leuchtenberg, and those of Volborth 

 of Sphceronites Leuchtenbergii and Protocrinites oviformis would 

 indicate the presence of arms in these also, although they have 

 not been actually obtained. In fact, branched grooves run from 

 the mouth over a great part of the calyx ; the branches of the 

 grooves however end in papillse of the calyx, which must be 

 regarded as points of origin of arms — a circumstance so much the 

 more remarkable, as it would follow that the arms of these Cystidece 

 must have had a position far removed from the mouth (Verhandl. 

 d. Konigl. Mineralog. Gesellschaft zu Petersburg, 1845-46, 

 Petersb. 1849). A specimen of Sphcsronites Leuchtenbergii in 

 Von BucVs collection agrees exactly with these figures. When, 

 in his second essay, L. von Buch founded the order Cystidecs 

 (1844), the oral arms of Echino-encrinus were already known. He 

 did not regard them as Crinoid arms, but called them feelers. 

 With a correct foresight he even then arranged the Pseudocri- 

 nites and Agelocrinus, with long arms passing from the oral part 

 of the calyx, among the Cystidece, but was not inclined to con- 

 sider these processes as true arms. He had even in 1840 termed 

 the remains of the three arm-like processes in Hemicosmites arms 

 or proboscides, but was led away from a just comprehension of 

 their nature by comparing them with oral tubes. 



In his beautiful monograph on the British Cystideans (Mem. 

 Geol. Survey, t. ii. Lond. 1848) Forbes has increased the num- 

 ber of forms with oral arms. He divides the Cystidece into, — 

 1st, those with arms : Pseudocrinites, Apiocystites, Agelocrinites ; 

 2nd, those with oral pinnulse : Prunocystites ; and 3rd, armless 

 forms : Caryocystites and Sphcsronites ; to which latter the Bri- 

 tish form Echino-encrinus is added. Forbes considers that the 

 arms observed by Volborth in the Russian species of Echino- 

 encrinus are oral pinnulse. The oral arms of Echino-encrinus and 

 Prunocystites are articulated in two series. Volborth observed 

 that in the former they are beset with small plates upon their 

 ambulacral surfaces, which he calls tentacles, remarking that 

 pinnulae are absent. These plates have the characters of mar- 

 ginal plates, which in the Crinoids {Pentaciinus) occur on the 

 arms as well as on the pinnulae. In Echino-encrinus angulosus 

 the remains of six arms were present. That this number does 

 not agree with the five depressions which usually surround the 

 mouth is explained by the fact, that the number of these facets 



