1:2 ARKIV FÖR ZOOLOGI. BAND 14. N:0 18. 



nevv genus in any of the two families. In the exteriör feat- 

 ures we have resemblances in the outline of the body, in 

 the position and structure of the sucker, in the position 

 of the genital openings. With some Eurylepiidce the absence 

 of marginal tentacles is a common feature. But one must 

 bear in mind that this characteristic is a negative one and 

 therefore too much importance is not to be attached to it. 

 The arrangement of the eyes is nearly of the same type, there 

 being marginal eyes at the frontal line as in AceroSy an Euryl- 

 eptid genus, and the cerebral eyes form two dusters (not so 

 well marked, it is true, as they are few both in Chromoplana 

 and Aceros) as in all the Cotyleans. It is certainly interesting 

 to find that the two pairs of large eyes above the brain, so 

 characteristic of Stylostomum and Aceros, are also present 

 here in Chromoplana, This must be an ancestral feature in 

 the two Euryleptid genera mentioned as well as in Chromo- 

 plana, as we also find a similar arrangement in Mullers 

 larva of the Pseudoceridce (as examples I may refer to Lang's 

 figures, 1884, Taf. 39, figs. 10 and 13 of the larva of Yungia 

 and Thysanozoon). Very young forms of Thysanozoon have 

 an arrangement of the eyes like that of Aceros (compare 

 Lang's Text figure 50 for Aceros with Taf. 39, Fig. 13 for 

 Thysajiozoon). As further evidence for the ancestry of this 

 feature, it may be mentioned that very young specimens of 

 the Prosthiostomidce also show a similar arrangement (Lang, 

 1884, Text fig. 51 A), which one would hardly expect from 

 the appearance of the cerebral dusters of the fuU-grown 

 specimens. 



It is, indeed, of great interest to find how such features 

 as the position, number and relative size of the eyes, whicli 

 at first one would not lay much stress on in settling system- 

 atic relationships, are retained with greatest tenacity in 

 the larval devdopment in the three different families Pseudo- 

 ceridce, Eurylepiidce and Prosthiostomidce. This cotylean larval 

 arrangement of the eyes, which is met with previously in 

 the f ull-gro wn specimens of only one cotylean species, Aceros 

 inconspicuus Lang from the Mediterranean Sea, is still kept 

 in the sexually mature specimens of this new genus from the 

 Pacific. It may be considered an ancestral feature. 



The coloration of Chromoplana is caused by real pigment 



