BASAL PLATES IN CRINOIDEA CAMERATA 509 



Stephanocrinus angulatus Conrad. University of Chicago paleontological 



Collection, No. 10787 

 No. 5. — Basal view, showing anchylosis and reduction of right-posterior 

 and posterior and sinstro-lateral basals, and compensating enlargement of 

 right-anterior basal. Basal formula, ea — bc—d—. Note reduction of right- 

 posterior and left-anterior radials. 



Platycrinus subspinosus Hall. Springer collection 

 No. 6. — Basal view, showing normal Platycrinus type of anchylosis. 

 Basal formula, ab — c—de—. To be compared with No. 5. 



Abacocrinus tesselatus Angelin. Springer collection, specimens having a 



hexagonal base 

 No. 7. — Basal view, showing asymmetry of posterior radials, enlarge- 

 ment and trunkation of posterior basal, and anchylosis and reduction of 

 antero-lateral basals, coupled with compensating enlargement of postero- 

 lateral basals. Basal formula, a — b — cd — e — . 



Melocrinus sampsoni M. and G. (type). University of Chicago paleontological 

 collection, No. 6958; probably Actinocrinus chouteauensis S.A.M. 

 No. 8. — Basal view showing reappearance of anterior basal suture. Basal 

 formula, ab — c—d — ex—. 



Batocrinus. University of Chicago paleontological collection No. 9082 

 No. 10. — Basal view of normal specimen. Basal formula, ab—cd—ex—. 

 No. 11. — Basal view of abnormal specimen, showing reappearance of 

 anterior basal suture. Basal formula, ab — c—d—ex—. 



Actinocrinus multiradiatus. University of Chicago paleontological 

 collection No. 8959 

 No. 9. — Basal view with base removed, showing asymmetry and reduc- 

 tion of posterior radials. Compare with Nos. 7-14. 



Steganocrinus pentagonus Hall. Springer collection 



No. 12. — Basal view of normal specimen, showing asymmetry and reduc- 

 tion of posterior radials. Basal formula, ab — cd—ex—. 



No. 13. — Basal view of abnormal specimen, showing loss of the antero- 

 lateral and posterior basal sutures and the reappearance of the anterior and 

 left-posterior sutures. Basal formula bc — dea—; factor x may or may not 

 be present. 



No. 14. — Basal view of another abnormal specimen, showing loss of right- 

 anterior basal suture and reappearance of anterior suture. Basal formula, 

 ab — c — dex—. 



No. 15. — Basal view of abnormal specimen, University of Chicago pale- 

 ontological collection, No. 8979, showing loss of anal plate. Basal formula, 

 b — cd — ea — . See Plate III. 



