ARKIV FÖR ZOOLOGI. 



BAND 14. N:o 13. 



Two new cotyleaii genera of Polyclads from 

 Japan and remarks on some other Cotyleans. 



By 

 SIXTEN BOCK, Uppsala. 



With 2 Plates and 6 Figures in the text. 

 Communicated November 9th 1921 by Hj. Théel and E. Lönnberg. 



During my stay at the Biological Station at Sagami 

 Bay, Misaki, in Japan, I met with two interesting turbel- 

 larians which, though genuine polyclads, closely resemble the 

 triclads in their habitus. I failed at first to detect their 

 true nature in the living specimen, as they were too opaque 

 to trace their internal organisation. 



Both species occur amongst Corallina in tide-pools or at 

 the low-tide limit. They were taken in May and June 1914. 

 They are among the smallest polyclads I have ever met 

 with. Their power of contraction is very slight and they 

 change the shape of their body extremely little. They seem 

 to be very slow in their movements. Both genera also agree 

 in having their dorsal surface pigmented, with an intense, 

 brown pigment which makes it impossible to trace the in- 

 ternal stucture. Ventrally they are unpigmented. Both are 

 of about the same size but their different marking makes it 

 very ease to distinguish them. 



Cliromoplaiia bella n. g. n. sp. 



This new species has its dorsal surface coioured in such 

 a way that at a glance it is easily distinguishable from all 

 other Polyclads (I, fig. 1). The dorsal surface is provided 



Arkiv för zoologi. Band 14. Ko 13. 1 



