232 Records of the Indian Museum. [VoL.- VII, 
The importance of a right estimate of the value of cephaliza- 
tion, as marked by the want of correspondence in the anterior 
limits of the dorsal and ventral setae, is apparent when we call to 
mind that this is one of the characters by which the genera of the 
Naididae are discriminated. Thus the segment on which the 
dorsal setae begin (reckoning the first segment with ventral setae 
as the second of the animal’s body) figures as a diagnostic mark 
of genera in Vejdovsky (17, p. 25), and in Michaelsen (8, p. 17). 
The extent anteriorly of the dorsal setae is the chief, if not the 
only, distinction between the genera Naidium and Nais. ‘To quote 
from a former paper (15) :—‘‘Beddard (2, p. 281), merging together 
a number of genera of other authors under the one name Nais, 
does so largely because they ‘agree in the important fact that 
the first five segments are cephalized,—that the dorsal setae 
do not commence until the sixth segment,’ and by implication 
would exclude from the genus any form which did not show this 
cephalization. Similarly Pristina and Naidium are united by him 
on the ground of the absence of this feature. Bourne (5) also 
believed that the number of cephalized segments is constant for 
the genus, and thought it probable that Devo furcata, possessing 
four achaetous dorsal segments, should on this account be removed 
from the genus, since the other members of it have five such 
segments.” And specially with regard to Branchiodrilus, ‘‘the 
presence of dorsal setae on all segments from the second onwards 
is mentioned as a feature in the generic diagnosis of Branchiodrilus 
in Bourne’s original paper (4), in Beddard’s monograph of the 
Oligochaeta (2), and by Michaelsen (8).’’ 
It is therefore evident that a distinction such as that which 
obtains between Branchiodrilus semperi and B. hortensis, where the 
dorsal setae begin on the second and sixth segments respectively, 
is held by most authorities as a ground for a generic separation. 
Holding this view myself, I accordingly separated the Lahore 
species as a distinct genus, Lahoria, though I thought it ‘‘perhaps 
worth while asking whether a cephalization which affects only 
the setal distribution (for the absence of gills on segments ii—v of 
the present form [i.e. B. hortensis] is evidently correlated with 
the absence of the setae which are necessary to stiffen them) has 
the systematic value hitherto generally attributed to it.’”’ 
It is to be added that the above view, of the absolute value 
of a different anterior extent of the dorsal setae as a generic 
character, has not always been strictly maintained. ‘Thus Michael- 
sen (8) unites into one genus Paranais three species known at 
various times as Naidium naidina, Paranais littoralis, and Uncinais 
uncinata, though their dorsal setae begin respectively on the second, 
fifth, and sixth segments. And in a recent paper (g) the same 
author prefers to include my Lahoria hortensis as a species of 
Branchiodrilus (as I do in the present paper), allowing the 
numerous close structural resemblances to over-ride the some- 
what artificial distinction based on the distribution of the dorsal 
setae. 
