PTEEOBEANCHIA. 

 CEPHALODISCUS. 



BY W. G. RIDEWOOD, D.Sc., LECTURER ON BIOLOGY AT ST. MARY'S 

 MEDICAL SCHOOL, UNIVERSITY OF LONDON. 



CONTENTS. 



Introduction ....... 



Diagnosis of a New Species of Cephalodiscus (C. hodgsoni) ..... 3 



Consideration of the Characters serviceable for the Discrimination of the Species of Cephalodiscus 3 



Review of the six Species of Cephalodiscus . ..... 7 



Key to the Identification of the Species of Cephalodiscus ..... .11 



Relations between Rhabdopleura and Cephalodiscus ... 12 

 Description of G. nigrescens 



Material ............... 20 



Tubarium ........ 20 



Polypides ........ 24 



Buccal Shield ......... 27 



Post-oral Lamella ........ 29 



Plumes . on 



* . . . V 



Stolon . oo 



. o* 



Coelom . qo 



...... oo 



General Internal Structure . . ...... 33 



Collar Canal Muscle ........ 41 



Alimentary Canal ....... 43 



Gonads .............. 45 



Buds and Budding ........ 47 



Description of C. hodgsoni 



Material ......... ^ n 



Tubarium ....... 50 



Polypides ............... 52 



Buccal Shield 



.............. 55 



Post-oral Lamella ...... . 57 



Gonads .......... 57 



Stolon and Budding ..... 59 



Buds ............... 61 



Summary of Results . ...... 62 



Literature on Cephalodiscus .... 63 



Explanation of the Plates ...... 65 



