348 ALFRED GIBBS BOURNE. 



that the peculiar character of the cephalization is a feature 

 amply sufficient to warrant the separate genus. 



Pterostylarides differs from all the other genera in the 

 constant possession of cephalic segments other than the peri- 

 stomial which are devoid of all setse. It is, of course, an assump- 

 tion that the region between the second and third seta- 

 bearing segments does represent two segments. Vejdovsky 

 in his ''Oligochseta " assumes that this is the case; but I 

 have not seen his paper on "Thierische Organismen der Zum- 

 menwasser von Prag, &c." In PL XXVI, fig. 1, which was 

 drawn from nature, there is but the very slightest external 

 indication of segments in this region, and I made no observa- 

 tions upon the septa. 



As stated above, in Bohemilla comata the setae in the 

 most posterior cephalized segment are few in number and very 

 small, and may disappear; when this occurs we have an undeni- 

 able instance of a cephalized segment devoid of all setae. Such 

 absence of all setae is, I think, to be regarded as extreme 

 cephalization.^ 



In the following description of P. parasita I have selected 

 from Vejdovsky^s description what seem the important points 

 in distinguishing this species from P. macrochaeta. 



1. P. parasita, O. Schmidt. 



Prostomial tentacle of about the same length as the peri- 

 stomial segment (" Mundsegment "). 



The eyes are on the dorsal side. 



The ventral setae of the second and third segments are curved 

 and crotchet-shaped, and about a third longer, and with longer 

 teeth than the ventral setae of the other segments. There 

 are five or six setae in these bundles, and seven or eight in 

 those of the other segments. 



The setae in the three most anterior dorsal bundles are 



' There can be no doubt that Chsetogaster, which in my opinion ought to 

 be classed with the Naidomorpha, presents a region correspondiug to two or 

 even three imperfectly developed segments devoid of seta; between the lirst 

 and second pairs of bristle bundles. — E. R. L. 



