82 THEEL, NORTHERN AND ARCTIC INVERTEBRATES. I. SIPUNCULIDS. 
(Fig. 50). Instead of true tentacles the oral disk is provided with some minute, irregu- 
lar, rounded elevations, or folds, the two dorsal ones being somewhat more prominent 
(Figs. 197.—201). I have not been able to perceive the presence of a contractile 
vessel, which, however, does not exclude the possibility of its bemg there. 
The place of insertion of the two ventral retractors is somewhat changeable. 
In some cases they are situated at the middle of the trunk itself, reckoning from the 
anus (Fig. 175); in other instances they are seen to be more behind, near to the 
posterior third of the trunk (Fig. 176). It may be stated that they are commonly 
attached slightly behind the middle of the trunk. 
With a few exceptions the interstice between the retractor-muscles is tolerably 
long in the species in question, the free posterior parts of them showing a not in- 
considerable length. But, as far as I have been able to see, those parts of them which 
have grown together are always longer than their remaining separate portions. The 
intestinal spiral bears on its outer surface a number of wart-like protrusions, is un- 
attached posteriorly, and shows about thirteen double circumvolutions. The oeso- 
phagus accompanies the united retractors until they become separated. The nervous 
cord terminates posteriorly with a small enlargement. 
Phascolosoma improvisum n. 
Pl. V. Figs. 51—58, PI. XTI. Figs. 177—182, Pl. XIV. Figs. 202—203. 
Total length of the largest specimen, 15 mm. Proboscis about half of the total 
length, or shorter. Trunk ecylindrical, slightly tapering anteriorly and behind. Tentacles 
absent and replaced by some irregular, rounded prominences on the oral disk. Skin 
hyaline and provided with distinct papille especially on the posterior end of the 
trunk and on the proboscis. A girdle of hooks always present. Two ventral retrac- 
tors, embracing the mnervous cord with their roots, and varying greatly in length. 
They are attached to the body-wall either at the middle of the trunk, or at its an- 
terior part or else considerably posteriorly. Two free segmental organs. Intestinal 
spiral composed of about 13 or more double turns, and not attached posteriorly. 
Body-cavity never contains eggs. 
Habitat: 
West Coast of Sweden: Elleskär together with Ph. Sabellarize. 
If the above diagnosis be compared with that of Ph. Sabellariz it will become 
evident that the two forms, though nearly related, differ mainly by two characters 
of importance, viz. by the presence or absence of hooks and papillae (Cp. Figs. 45—49 
and Figs. 51—58). 
The true proportion between the proboscis and the trunk, reckoning from anus, 
is not easy to state exactly. It seems as if the proboscis of Ph. improvisum is 
somewhat longer than that of Ph. Sabellarizxe, and that, in some cases, it is as long 
as the trunk itself, or longer still, which may depend upon different states of con- 
