of the Crinoidea brachiata. 409 



number of Pentatremites of various species, and could also be 

 demonstrated in some specimens of Elceacrinus and Codo- 

 naster. 



The Cystidea are generally not well fitted for such investi- 

 gations, because in them the radii, ventral covering, and ver- 

 tical aperture are not separated from each other, as in the 

 Brachiata. Only the two genera Stephanocrinus and Crypto- 

 crinus^ which depart so widely from the other Cystidea by the 

 want of calycine pores and their simple regular structure, 

 could be taken into consideration. 



Stephanocrinus has almost exactly the same composition as 

 Pentatremites^ and is essentially distinguished only by the free 

 development of the radii ; the lateral pyramidal orifice, on 

 account of which the genus is referred to the Cystidea, has the 

 same position as the lateral vertical aperture of the Blastoidea. 

 The investigation of some well-preserved specimens from 

 Lockport, for which the collection is indebted to M. Roemer, 

 showed that, with similar orientation, the dorsal axis also has 

 the same position as in Pentatremites. 



In Cryptocrinus the symmetrically tripartite pentagon to 

 which the stem is attached is immediately followed by a re- 

 gular quinquepartite circle, above which the pyramidal vertical 

 aperture is so placed that the two inferior circles may be 

 compared to the dicyclic tri- 

 partite base of a Brachiate 

 Crinoid. If, in accordance with 

 this, we place the pyramidal 

 aperture as the pole of a radial 

 axis, the dorsal axis (as shown 

 in the annexed figure) runs 

 from the left adjacent side to 

 the right abjacent angle of the 

 pentagon. The position stands 



in the same relation to the axis ^ , 



- , _,, -1 ,1 • G-yptocnnus. 



of the Blastoidea as the axis 



of Melocrinus to that of Platycrinus or Taxocrinus — namely, 

 towards the same side, but turned by one decimal space fur- 

 ther from the radial axis. 



The results of the observations upon the symmetrically di- 

 vided base of the Crinoids here communicated may be summed 

 up in the following propositions : — 



1. In all Crinoids in the calyces of which the radii may be 

 arranged in accordance with a radial, and the parts of the base 



Ann. (t Mag. N. Hist. Ser. 4. Fo ?. vii. 30 



