rLATYCRINID.T:. PLATYCRIXUS. 3 3 



skeleton. Miller founded his opinion on the belief that according to the various positions 

 of the rays, the muscles became developed in corresponding degrees. It so happens 

 however that we have specimens with the rays perfectly closed, others with them partly 

 so, and others with the rays spread to their full extent, and no alteration whatever is 

 observable on the surface, on either those species with smooth plates, or on those with 

 highly ornamented exteriors. 



On referring to our illustrations, the very great difference in the form of the perisomic 

 plates in the two species will at once be manifest. Another decided specific ditlerence 

 in the P. tnginlldactylus is its central elongated oral tube ; whereas the mouth of the 

 rugosus is not proboscidial, though Miller asserts that it is. 



We have obtained numerous specimens of the P. trigintldactylus in strata of the 

 mountain limestone, where but few indications of the rugosxts exists. The P. triginti- 

 dactijlus attained a larger growth than the typical species. We have collected specimens 

 superior in size to the beautiful and well preserved specimen, the figure of which is 

 given in our third plate. It was only equalled or surpassed in size by the P. gigas. 



Miller in his second plate o( AclinocriuUes, page 98, Crinoidea, gives the figure 

 (7) of what he terms the proboscis oi Acthwcrinites triacontadachjlus. The smoothness 

 of these proboscidial plates, in contrast with some pointed abdominal plates which he 

 had met with, gave him an opportunity of further indulging in his favorite theory as 

 to the muscularity of the calcareous frame work of these animals. At page 102 he 

 adduces the specimen referred to as proof in support of his views. Unfortunately for 

 his hypothesis the specimen does not belong to tlie genus Actinocrinus at all. It is in 

 fact the oral tube of a Platgcrinus, that of Plalycrinus trigintidaclylus. 



6. Species. Platycrinus Granulatus. (Miller.) 

 PL III. Jig. 2, i. to o. 



Definition. — Abdominal bulb globose. Dorso-central plate pentagonal and entire, 

 and centrally striated for the articulation of the column, with a circular perforation 

 communicating with the columnar canal. Perisomic plates five, beautifully embellished 

 with granulpe, as are all the other plates. Mouth central and elongated. Rays thirty- 

 live. Column slender. 



F 



