59 
new ones from Japan together with Pr. grande Stimpson (Yeri & 
Kaburaki, 1918 and 1920). Enchiridium contains only one species, 
E. periommatum Bock from the West Indies. 
All the Prosthiostomum-species that have been closely examined 
agree anatomically very well with Pr. siphunculus (Delle Chiaje) 
described so extensively by Lang. The genital organization shows 
particular agreement with the type, and the diagrams and descrip- 
tions given verify the pronounced homogeneity. There are also 
other features of the organization so far known that indicate that 
all the species are closely related. As the species under consideration 
' dilfers from the Prosthiostomum-species known to date, precisely in 
(those characteristics that are, as far as we know, common to them 
all, I feel that it would be premature to rank it with the same genus 
as these. In order to stress the very close relationship with the 
genus mentioned, I have called the new genus Euprosthiostomum. 
I wish particularly to emphasize that the raising of the new species 
to generic rank is based less on the importance of the differentiated 
i characteristics than on the faet that the characteristics of Prosihi- 
! ostomum have been found to be common to a considerable number 
of species. The system should show the direct mutual connection 
between species. Therefore, it would certainly be out of the 
question to introduce into a genus as homogeneous as Prosthiosto- 
mum an element so different as the new species. 
The feature in the new form that particularly catches one’s 
eye is the location of the sucker relatively near the caudal end of 
the body; it is therefore at quite a distance from the centrally 
located female gonopore. In the Prosthiostomum-species, on the 
other hånd,« we find the sucker just back of the female pore, in 
or near the median point of the ventral side. It is only in Pr. 
pulchrum Bock, that one can speak of any noticeable backward 
displacement and it is then in direct connection with the removal 
of the genital pores from the vicinity of the pharynx. In Enchiri¬ 
dium the sucker lies anterior to the median point of the body, 
likewise close to the female opening. The unusual development, 
as well as the remarkable change in location of the sucker, must 
be connected with the animai’s way of living, which has already 
been treated above. Although a splendid characteristic for species, 
it would, nevertheless, in itself be insufficient as reason for 
