160 On a new Species of Thamnodrilus. 
the body; but I believe that I missed another segment in 
this region of the body, also a very narrow one and apt to be 
confused in the larger example with the peristomium and 
the immediately succeeding segment. It is clear in the 
smaller example. 
The smaller specimen, however, is not only smaller, but 
apparently more contracted by the preservative reagent 
(corrosive sublimate followed by alcohol). Thus the segments 
stand out, and I think that this specimen gives a_ plainer 
picture of the normal conditions. In any case the tubercula 
pubertatis occupied precisely the same number of segments in 
both worms—i. ¢é., six (on segments 22-27). In the smaller 
specimen the tubercula formed a furrow which was flattened 
out in the larger to give the appearance described above in 
Th. cognettii. The organ was continuous throughout the six 
segments and just overlapped the seventh in the larger worm. 
Anteriorly it curved inwards, but was perfectly straight in 
the five last segments of those upon which it was developed. 
In my original account I did not note the tubercula; but they 
are given by Michaelsen in his table of the characters of the 
species of Thamnodrilus already referred to. This writer, 
however, gives segments 21 to 26 as their range. This is in 
accord with my original mapping of the clitellum. From 
the commencement of the tubercula the clitellum extends 
forward to the beginning or middle of the seventeenth segment. 
So late a commencement of the clitellum is not common in 
the genus Thamnodrilus, though it is much more common for 
the clitellum to extend back, as it does in the present species, 
as far as the twenty-seventh. However, in the three species 
Th. riveti, Th. tuberculutus, and Th, potarensis the clitellum 
begins in the seventeenth, or even in the eighteenth. The 
sixteenth isa very usual segment to be the first of the clitellar 
series ; but I cannot reconcile this with the segmentation 
already referred to. ‘The clitellar modification of the twenty- 
seventh segment appears to occupy only the anterior half of 
the segment. 
In view of the absence of the lateral pairs of sete in 
Th. cognettii (and in several other species), I may remark 
that I have correctly figured their presence in my paper upon 
Th. gulielmi. 
I endeavoured to ascertain the presence or absence of 
papille, similar to those of Th. cognettii, in the present 
species, but without avail. ‘There appear to be none. The 
matter is important, because Michaelsen and Cognetti come 
to quite different couclusions on the frequency of such 
papilla. Michaelsen mentions them in a few species only 
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