III. Thenarocrinus calUpygus. 



227 



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

 Holcroft, one branch has only 3. 



Pahnars vary quite irreguharly from 4 to 10. 



The various series of Postpalmars are likewise irregular in 

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

 average about 14. 



<(/3!r' 





DIAGRAMS OF THE STRUCTURE OF THENAROCRINUS. 



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

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

 anal, f = Costals, f/= Distichals, ;o=Palmars. (x 2.) 



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



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



Diagr. 4. Edges of plates in ventral sac, to show folding, (x 5.) 

 Biagi'ams 2, 3, and 4 are all taken from specimen 57478 b. 



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

 articular radiating striae. ( 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 irregularity of growth indicating a radial 

 suture, (x 4.) 



Diagr. 8. Weathered 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, from 

 57478 ^.. (Xl2.) 



A rough calculation from these data makes the total num- 

 ber of arm-ossieles 48,290. Parkinson * calculated the 

 ossicles of the arms and pinnules in Encrinus fossilis, Blura- 

 enbach ( = -£". Uluformis, Lamarck), as 26,660, but half that 



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



