NOTES ON THE GENUS MONSTRILLA. 573 
cord is continued posteriorly as a flattened band, the double 
nature of which is shown by its dumb-bell shape in section. 
There is no trace of ganglionic enlargements. The cord may 
be traced as far back as the fifth thoracic segment, where it 
thins out and disappears. 
Such is the general organisation of this remarkable genus. 
The determination of the species included in the genus is 
a matter of considerable difficulty, as the earlier descriptions 
are deficient, and it is in some cases difficult to make an 
accurate determination from the representations of the animal. 
Dana’s Monstrilla viridis appears to be identical with 
the specimen described by Semper, both being characterised 
by the mouth being situate in the middle of the thorax. 
Monstrilla anglica, Lubbock, and M. helgolandica, 
Claus, resemble one another in having six sete on each 
member of the furea, and differ in the number of abdominal 
segments, and apparently in the characters of the antenne, 
which are very long in Lubbock’s figure. I regard M. 
anglica as identical with Thompson’s Cymbasoma Herd- 
mani, and with the specimens, all males, which I have re- 
ceived from Sinel, from Jersey. M. helgolandica, I am 
inclined to think, is identical with Scott’s specimens, relying 
on the characters of the antenne and the position of the 
mouth, but the latter have four abdominal segments, whereas 
Claus only describes three. This may be explained by the 
fact that Claus’ specimens are young, as appears to be the case 
from his figures and description. 
Claparéde’s figure of the female of M. Dane shows three 
sete on each furcal member and three abdominal segments. 
I regard it as identical with a specimen found by myself at 
Plymouth on October 24th, and with two specimens sent by 
Sinel from Jersey. All these are females, and are charac- 
terised by the elongate cephalothorax and the relative narrow- 
ness of the body. Claparéde’s male clearly belongs to another 
species; he figures four setee on each furcal member, but, 
judging from the specimens in my possession, there must be six, 
and he has omitted to count them carefully. Nor does he 
