Fort-Major T. Austin on the Genus Platycrinus. 91 



By the proposed arrangement the two genera would stand in 

 the following order. 



Platycrinus. 

 Platycrinus Icevis. Platycrinus trigintidactylus. 

 striatus. spinosus. 



elongatus. 



The generic formula of Platycrinus would be as follows : — 

 Central dorsal plate pentagonal, whole and undivided ; lateral 

 or perisomatic plates five; ventral dome or proboscidiform 

 mouth (?) elevated, rising in the centre to a column of some 

 considerable height. 



The formula of the dorsal part of the proposed new genus 

 resembles Platycrinus in the number of lateral plates, but in 

 shape they are somewhat different. The upper or ventral 

 surface, however, is quite dissimilar, and presents a striking- 

 contrast to the elevated ventral elongated cone of Platycrinus — 

 it being covered in with four, five, or more plates which are 

 only slightly elevated above the upper margin of the periso- 

 matic or lateral dorsal plates, while the mouth, anal orifice, or 

 whatever its office may have been, is situated in the widest 

 interradial space, and it is mostly on a level with the base of 

 the arms, but never in the centre of the dome, and it could 

 have been but slightly protruding. 



It is proposed provisionally to name the new genus Medusa - 

 CRINUS ; and it contains the following species : — 



Medusacrinus mucronatus. Medusacrinus mammillatus. 



rtigosus. ■ granulatus. 



tuberculatus. 



The accompanying drawings of a specimen of each genus 

 will convey a better idea of their characters than any written 

 description. In each case they are represented without arms. 



Platycrinus Icevis. Medusacrinus mucronatus. 



a. Anal or oral tube. b. Mouth or aual orifice. 



