TIT. Thenarocrinus calUpygus. 



227 



witli 5, 2 with 6, 1 witli 7, aiul in the young specimen, 293 

 Ilolcroft, one biancli has only ."3. 



Pahnars vary quite irreguhuly from 4 to 10. 



The various series of Postpahnars are likewise irreguhir in 

 number, the observed extremes being 6 and 18, and the 

 average about 14. 



«B3r' 





% 9 



DIAGRA.AIS OF THE STRUCTURE OF THENAROCBINUS. 



Diagr. 1 . The aual plates and lower part of the ventral sac, composed 

 from the evidence of six specimens. R' = Radianal, X =Brachi- 

 anal, c = Costals, r/=Distichals, /tJ = Palmars. (x 2.) 



Diagr. 2. Plates from halfway up ventral sac. ( X 4.) 



Diagr. .3. Plates from distal end of sac. ( X 4.) 



Diagr. 4. Edpes of plates in ventral sac, to show foldinp-. ( X 5.) 

 Diagi'ams 2, .'», and 4 are all takpn from specimen 57478 h. 



Diagr. 5. Section of stem showing sutures, large pentagonal lumen and 

 articular radiating strife. ( X 3.) 



Diagr. 6. Dissection of dorsal cup. (Nat. size.) 



Diagr, 7. Some proximal stem-ossicles of 293 Holcroft, showing alter- 

 nation of size, and ii'regularity of gi'owth indicating a radial 

 suture, (x 4.) 



Diagr. 8. '\^'eathered arm-ossicles of 138 Mason College, with indications 

 of an axial canal, seen from dorsal surface. ( X 6.) 



Diagr. 9. Ventral surface of arm, showing rounded elevations, fi-om 

 57478 b. ( X 12.) 



A rough calcuhition from these data makes the total num- 

 ber of avm-ossicles 48,290. Parkinson * calculated the 

 ossicles of the arms and pinnules in Encrimis fossilis, Blum- 

 enbach { = E. Uliifurmis, Lamarck), as 26,660, but half that 



* ' Organic Remains &c.,' ii. 181 (London, 1808). 



