227 
III. Thenarocrinus callipygus. 
with 5, 2 with 6, 1 with 7, and in the young specimen, 293 
Hoi croft, one branch has only 3. 
Palmars vary quite irregularly 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. 
DIAGRAMS OF THE STRUCTURE OF THENAROCRINUS. 
Diagr. 1. The anal plates and lower part of the ventral sac, composed 
from the evidence of six specimens. R' = Radianal, X = Brachi- 
anal, e = Costals, e?=Distichals, ;? = 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. Edges of plates in ventral sac, to show folding. (X 5.) 
Diagrams 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 alters 
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 b . ( X 12.) 
A rough calculation from these data makes the total num- 
ber of avm-ossicles 48,290. Parkinson * calculated the 
ossicles of the arms and pinnules in Encrinus fossilis , Blum- 
enbach ( = E. liliiformis , Lamarck), as 26,660, but half that 
* 1 Organic Remains &c./ ii. 181 (London, 1808). 
