of the Crinoidea brachiata. 401 



over from the right adjacent radius to the left abjacent inter- 

 radius. This expression will remain the 

 same when, the calyx being placed erect, i ^ 



the vertical aperture is directed back- I / 



ward. y\\/ 



A dicyclic tripartite hose is possessed y^ \ /\. 

 by the family Taxocrinida3, to which Taxo- \ 

 crinus^ Forhesiocrinus^ Ichthyocrinus^ Me- \^^ 

 spilocrinus^ and Lecanocrinus are to be \ , 



referred. V— 



The above-mentioned five genera are / 

 nearly allied to each other, both by the ,/ 

 similar composition of the base and by T>L,t„„ .,-.. » 



1 /* 1 " !•• ml 1 linytl ItltlS, 



the structure ot their radii, ihe latter 

 divide repeatedly, but retain uniserial joints, on the sides of 

 which distinct marginal plates are sometimes visible, but no 

 pinnules. In none of them has a perfectly preserved ventral 

 covering with the vertical aperture been observed; but the 

 polar interradius is usually indicated by the circumstance that 

 the ventral covering descends between two radii to the base, 

 so that the subjacent segment of the upper basal circle acquires 

 a form diiferent from that of the other segments of the circle. 

 One or more inten-adial plates make their appearance in the 

 polar interradial space (and sometimes others in the lateral 

 interradii) ; but they did not serve as a firm shelly union of 

 the radii, which retained the power of movement by means of 

 chamfered joints as far as the first radial segment. The 

 family is most nearly allied to the Poteriocrinidse, to which 

 Poteriocrinus, Cyathocrinus^ and other similar genera with a 

 dicyclic, regularly quinquepartite base belong. 



The genera Taxocrinus and Forhesiocrinus are so nearly 

 related that it is a question whether both can be maintained. 

 Phillips, in 1841, first miited fom- Crinoids previously described 

 as belonging to Cyathocrinus and PoteriocrinuSy on account of 

 the concordant structure of their radii, under the name of Iso- 

 crinus, which has since become Taxocrinus. Forhesiocrinus 

 should be chiefly distinguished, according to De Koninck, by 

 the presence of interradial segments. The genera, however, 

 can only be retained if Taxocrinus be limited to those species 

 in which the first division of the radii takes place in the third 

 joint, whilst four primary radial segments are characteristic of 

 Forhesiocrinus. To Taxocrinus thus limited belong the Eng- 

 lish T. tuherculatus^ the American T. inter scapular is ^ and the 

 two Rhenish species, T. rhenanus and T. affinis. The other 

 species placed in the genus by L. Schultze are either to be re- 

 moved or doubtful. 



