1893 - 94 .] Dr Gilchrist on Pallial Complex of Dolahella. 265 
such an interesting and instructive study, and it is in this respect 
that the specimen under examination is of value. 
The animal is 4J inches long by 2| broad. It is much wider 
posteriorly than in front (fig. 1). The general surface of the body, 
not excepting the rhinophora, is covered with small filamentous 
protuberances. In many of the other species examined these were 
much more strongly developed. They were also found in some of 
the Notarcliidce, a group which, as we shall see, resembles the 
Dolahellidoi in other respects. The whole posterior part of the 
animal presents the appearance of an oblique truncation, round the 
margin of which these filaments are specially developed. 
Anteriorly the head region is well marked, with fore and hind 
tentacles. 
The posterior and broader part consists externally of the highly- 
developed parapodia (pa.). These lateral extensions of the foot 
have grown upwards on either side and behind, so as to enclose 
almost completely the visceral region, consisting of viscera, mantle 
gills, and other pallial organs. The only part of the visceral region 
visible is the exhalent sipho (ex.s.) and part of the mantle (m.), 
which protrude slightly through the small parapodial opening. 
There is thus formed a large sac-like cavity round the visceral 
region. As will be seen from fig. 2, a cross section of the animal, 
somewhat diagrammatic, this cavity extends in under the viscera 
both at the sides (fig. 2) and behind, (fig. 3), — a condition also 
characteristic of the Notarcliidce, and which may be of importance 
as indicating a persistence of the prosobranchiate condition where 
the visceral mass is quite free from the foot. 
In Notarclius the parapodial opening is even further reduced, 
being indeed limited to a mere aperture in front, one opening serv- 
ing both as inhalent and exhalent sipho. Though the parapodial 
opening is not so far reduced in Dolahella, there are special arrange- 
ments by which exactly the same physiological condition may be 
temporarily brought about. Fig. 2 shows that the parapodia {pa.) 
are specially modified at their free borders, so that they can be 
firmly interlocked ; and there is on the posterior end of the visceral 
mass a cushion or button-like protuberance by which the posterior 
end of the parapodial opening can be securely closed, there being 
thus left only the wide and well-marked opening in front. The 
