16 



W. (t, RIDEWOOD. 



The red line of the shield which is so conspicuous and constant a feature of 

 Cephalodiscus does not seem to l)e present in Rliabdo'pleura. Bchepotieff shows, in 

 the exact position occupied l)y the red line in Cephalodiscus, a " Pigmentstreif " (1904, 

 pi. 2, fig. 9, and 1905, p. 796, fig. l), 1>ut since he says nothing about red colour, one 

 is led to conclude that the pigment-stripe is black. The crowd of black pigment spots 

 at the anterior point of the shield of Ehabdopleura, assumed to be a rudimentary organ 

 of vision, finds no equivalent in Ceplialodiscus. The relations of the shield to the 

 mouth, however, and the great mol)ility of the shield, and the glandular nature of 



Text-Figcke 8. — Rhabdoplcura nannani, a polypide greatly enlarged. (Copied from Lankester, 13, plate 38, 



fig. 1.) 

 a, mouth ; b, anus ; c, polypide stalk ; d, buccal shield ; c, plume ; /, visceral mass. 



the thick central part of the ventral wall of the shield (Schepotieff, 1905), are the 

 same in both Rhahdopleura and Cephalodiscus. 



The collar region is produced in both into a postoral lamella and plumes. The 

 latter are two in numljer in Rhahdopleura, and although Cephalodiscus has in most 

 cases four pairs or more, Harmer's discovery of male polypides of C. sibogae with one 

 pair of plumes only (10, p. 84) is of interest in this connection, in spite of the fact 

 that such plumes do not possess pinnules. 



