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



varies ; Von Buch states that there are five or six ; and I possess 

 a specimen with eight round depressions about the mouth, which 

 are united with the mouth by grooves. Echino-encrinus striatus 

 possesses, according to Volborth, together with a vei*y much 

 narrower pointed oral extremity of the calyx, only two much 

 larger opposed oral arms, which have the same structure as in 

 Echino-encrinus angulosus. From their relations, however, it is 

 probable that these are not pinnulse, but arms; for it is not 

 usual for pinnulse to be isolated. If they both belong to a single 

 ambulacrum, how are we to imagine a single ambulacrum in this 

 locality in the immediate neighbourhood of the mouth ? If, how- 

 ever, they belong to two different ambulacra, they can, as soli- 

 tary structures, be only arms. 



The arms of Echinosphcerites aurantium, Wahlenb. [Sphcero- 

 nites aurantium. His.) have essentially exactly the same relations 

 as Volborth has described and figured. In such well-preserved 

 specimens as now lie before me, the origins of three articulated 

 arms at the oral region of the calyx are recognizable. The five 

 uppermost calycine plates are raised into a three-sided pyramid 

 transversely truncated above, whose obtuse edges are prolonged 

 into the arms. Two sides of the pyramid are broader than the 

 third. The sutures between the five pieces are so disposed that 

 two of them are situated upon the broader side of the pyramid, 

 the three others in the obtuse edges. Two supplementary pieces, 

 however, are added to the five principal portions of the pyramid, 

 and extend from the calyx into two of the angular sutures. The 

 pore-grooves of the plates of the calyx extend only on to the 

 lower portion of the circumference of all the seven pieces. The 

 arms immediately subdivide again. From the oral aperture 

 grooves, beset with marginal plates, pass on to the arms. For 

 the rest, the division of the arms shows that they are arms, and 

 not pinnulse. Whether these arms, like those of a few other 

 Cystideans, as Pseudocrinites, were provided with articulated 

 pinnulse, cannot be decided, since they are broken short off. 

 Whether the Cai^yocystites possessed arms is not as yet known, 

 but it can hardly be doubted, since they are not certainly distin- 

 guishable from Echinosphcerites. 



In Hemicosmites, three of the six uppermost plates of the calyx 

 are provided with an insection, which arises from the triradiate 

 median calycine opening. Each of the insections is continued 

 into a groove ; the groove terminates after a slight expansion in 

 an elevation of the calyx which served for the attachment of an 

 arm. The elevation no longer lies on the plates of the upper- 

 most, but upon three of the plates of the second series. The 

 elevation exists only in specimens which are not worn down, and 

 is beautifully obvious in a specimen which M. Ewald has sent 



