PLATYCRIXID.E. PLATVCRTXUS. 4 1 



The Meso-plates — Are not well defined in the generality of specimens. They are 

 hexagonal with a central tubercle on each. 



The Abdominal Plates — Are irregularly hexagonal with one or more tubercles 

 on each. 



The Mouth — ^Is unobtrusive. Though Miller asserts that the integument over the 

 abdominal cavity was " capable of elongating itself in the centre into a proboscis, 

 analogous to that in Actinocrinites." This is quite erroneous for in all those species 

 which have large, or e^en moderately sized abdominal plates, the mouth is in\ ariably 

 incapable of elongation to the extent Miller supposed it to be. In species where the 

 abdominal plates exceed certain limits as to size, the mouth is either sub-central or lateral. 

 It is evident from the structure of the adjacent parts that such must always be the case. 



The Rays — Amount to thirty, and are furnished with plumose tentacula similar to 

 those of others belonging to the genus. 



The Column — Is more massive than in other species of Platicrini, but subject to the 

 same modifications as observed in the typical species. Small tubercles sometimes occur 

 on the extreme ends of the elliptical columnar joints. 



The Auxiliary Side Arms — Appear to have been small, and placed at irregular 

 intervals along the column. 



Base of Attachment — Unascertained. 



There are greater variations in form observed in this species than in any other of the 

 Platycrini. None of the specimens however depart sufficiently in character from the 

 best defined, to constitute specific difference. 



11. Species. Platycrinus tuberculatus. (Miller.) 

 PL IV. fig. .3, m, toy. 



Definition. — Dorso-central plate pentagonal and tumid ; perisomic plates short, with 

 the articulations for the rays rather low ; abdominal plates conical in their centres ; 

 mouth lateral, and unobtrusive ; rays and column unkiaown. 



G 



