PLATYCRINID.E. rLATYCRINITES. 31 



Synonymes and References. 



Platycrinitcs trigintidactylus. — Messrs. Austin, Ann. Sf Mag. Nat. Hist. Nos. 63 and 



69, pages 109 and 199. 



Formation and Localities. 



Carboniferous limestone. — Clevedon, Somerset; Black Rock, Avon side, Bristol; 

 Hook Point, County of Wexford. 



Description of the Calcareous Frame Work. 



The Dorso-central plate. — Saucer shaped, with gentle undulations between the 

 angles of the pentagon for the adhesion of tlie slightly orbicular edges of the perisomic 

 plates. 



The Perisomic plates — are broad and smooth, with the lower edges sUghtly 

 orbicular, by which they fit into the shallow undulations in the edges of the dorso- 

 central plate. Tlie five perisomic plates are proportionally broader than has been 

 observed m either the Icevis or sjjhiosus. It should be remarked that the edges of these 

 ])lates, as well as those of the dorso-central plate, in all the species examined are finely 

 striated for the purpose of adhesion. The perisomic plates are so deeply indented by 

 the excavations for the basal joints of the rays, that the rays appear to spring fi'om the 

 centres of the plates, instead of resting on their upper edges as in the typical species. 

 A transverse ridge crosses the bevelled edge of each excavation, as in the Icevis, but 

 there is in this species a faint indication of a perforation below the aperture, through 

 which the muscles of the rays passed. 



The Abdominal plates. — These plates are smooth, and apparently hexagonal. 



The Proboscis. — From the centre of the abdominal plates rises the elongated oral 

 tube, which is protected hy numerous hexagonal plates. This organ is less produced, 

 and the proboscidial plates smaller than in the tj-pical species. 



The oral aperture is quite covered over with ii-regular shaped plates, which may be 

 considered in the light of so many valves, though not strictly such. The mouth was 

 c\ idently so formed, that when closed the plated uitegument passed completely over it. 



