396 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
It is not unlikely that such highly modified forms as Polynoe 
lordi , P. pulchra , and P. fragilis have descended from Harmothoe 
stock and do not rightly belong in the genus Polynoe. The 
characters are a melange of those of Harmothoe and Polynoe (sensu 
ext.). This may be taken to indicate that these commensals retain 
characters of the Polynoid ancestor from which typical Polynoe 
and Harmothoe have both descended. The structure of the pro- 
stomium, especially the presence of basal joints to the antennae, 
recalls Harmothoe ; while the structure of the foot is more like 
that of Polynoe. The sequence of the elytra differs from that of 
both genera. These species certainly do not belong in the genus 
Lepidasthenia , where Darboux (’99) has placed them. 
The asymmetrical somites (dorsal cirrus on one side, elytra on 
• the other) constitute the most striking peculiarity of this species, 
and one which, so far as present knowledge goes, it shares only 
with Polynoe gigas Johnson (’97, p. 174), Lepidametria com- 
mensalis Webster (’79, p. 210), and Polynoe lordi (Baird). In 
Polynoe gigas , I have found at most two unsymmetrical somites; 
in P. lordi , from one to nine ; for Lepidametria the number is not 
stated. In two specimens of Harmothoe tuta I have found, 
respectively, 15 and 16 asymmetrical somites! As in P. gigas , 
they are confined to the posterior part of the body (back of the 32d 
somite) whence the sequence of the elytra differs in different 
individuals. In the older specimen (Columbia University collec¬ 
tion) there are 38 elytra on the right side and 35 on the left. In 
the younger specimen (No. 963) there are 38 elytra on the right 
side, 36 on the left. The asymmetrical somites of the former are: 
38, 41, 43, 56, 57, 60, 61,65, 69, 71, 77, 80, 81, 82, 83 —a total of 
15 ; those of No. 963 are: 33, 37, 38, 39, 40, 41, 43, 45, 60, 62, 64, 
66, 68, 70, 72, 74 — 16 in all. 
The identification of the specimens from Puget Sound with the 
Polynoe tuta of Grube (’55), described from specimens collected 
at Sitka, seems reasonably safe, although his description takes no ac¬ 
count of the diagnostically important structures of the head. The 
sequence of the elytra up to the thirty-second somite is precisely as 
stated by Grube. Beyond that point it differs in every different 
individual — a fact not perceived by Grube. 
In no Polynoid has a normal asymmetrical somite been found in 
front of the 32d. 
