THE OTTAWA NATURALIST 



VOL. XXX. OCTOBER, 1916. Xo. 7 



COMAROCYSTITES AXD CARYOCRINITES 



Cystids with pixxuliferous free arms. 



By A. F. Foerste, Daytox, Ohio. 



IXDEX 

 I. Preliminary remarks on the arm structure of crinoids and cystids. 



1. The origin of biserial arms. 



2. Uniserial arms and pinnules in Comarocystites. 



3. Biserial arms and brachiolar pinnules in Caryocrinites. 



4. Biserial brachiolar pinnules in Stephanocrinus. 



II. Detailed description of Comarocystitf.s punctatus Billings. 



5. Chief characteristics of the theca. 



6. The numbering of the rays of the food-groove system. 



7. The thecal plates bordering on the transverse apical food-groove. 



8. The location of the hydropore. 



9. The covering plates of the transverse apical food-groove. 



10. The anal pyramid. 



11. Fixity in the arrangement of the thecal plates limited to the immediate vicinity of 



the transverse apical food-groove and of the anal pyramid. 



12. The arrangement of the basal thecal plates. 



13. The structure of the thecal plates. 



14. Sections across the anal pyramid and the transverse apical food-groove. 



15. The arms of Comarocvstites punctatus. 



16. The pinnules. 



17. The absence of food-grooves on the brachials. 



18. The column or stem. 



19. Geological horizon and geographical distribution. 



20. Literature on Comarocvstites punctatus. 



III. Detailed description of Comarocystites shumardi Meek and \Yorthen. 



21. Comarocystites shumardi. 



22. The so-called variety obconicus. 



23. The structure of the thecal plates. 



24. Horizon and distribution. 



25. Literature on Comarocystites shumardi and obconicus. 



IV. General remarks on Comarocystites. 



26. The zoological position of Comarocystites. 



V. Addenda. 

 2 7. Xotes on Caryocrinites omatus Say. 

 2 8. Acknowledgments. 



I. Prelimtxary Remarks ox the Arm Structure of 

 Crixoids axd Cystids. 



1. The origin of biserial arms. According to Dr. F. A. 

 Bather (Caradoeian Cystidea from Girvan, 1913, p. 385), "the 

 brachioles of Blastoids and Cystids differ from the Crinoid braeh- 

 itvm. not merely in more fundamental features, but also in the 

 fact that they are invariably biserial and present no trace of 

 an anterior uniserial stage." The crinoid arm. on the contrary, 

 is regarded by Bather (Echinoderma, 1900, p. 116), to have 



