234 ARTHUR E. SHIPLEY. 
the genus at present comprises three species, all found on the 
north-west coast of the Scandinavian peninsula. 
The species differ considerably in size. O. Steenstrupii, 
whose body measures but 3 mm. in length, is the smallest 
Gephyrean hitherto described, and, corresponding with its 
minute size, the structure of the body is very much simplified. 
O. Sarsii attains a body length of 8 mm., whilst the body of 
O. glaciale is 85 mm. long. I have hitherto been unable to 
obtain specimens of the two last-mentioned species; but, 
thanks to the kindness of Professor EH. Ray Lankester and 
Canon Norman, I have been enabled to investigate the struc- 
ture of the smallest species, of the minute anatomy of which 
the following is an account. 
Tur ExterRNAL APPEARANCE. 
In the better preserved specimens the body was about 3 mm. 
long, pointed behind, and in front passing abruptly into the 
introvert (figs. 1 and 2); some, however, which were not well 
preserved, and which did not appear to be normal, had a longer 
and more slender body, which passed gradually into the intro- 
vert. The length of the latter structure varied in accordance 
with the amount of its protrusion : it was, when fully extended, 
almost invariably coiled up, and consequently difficult to 
measure, but in no specimen was it 34 mm. long, the length 
described by Koren and Danielssen. 
The skin is of a French grey, almost greenish colour, and 
is divided into small areas by numerous crinkles, which at 
the posterior end of the body cross one another almost at 
right angles; in some cases such folds of the skin occurred 
at more or less regular intervals round the proboscis, giving 
it a superficial appearance of being segmented (fig. 1). 
The introvert is covered with papille, which, according to 
Koren and Danielssen, are disposed in regular rows. The 
nature of these organs, which correspond with the papille of 
the larger Sipunculids, will be described below; they open to 
the exterior, but the opening is not always situated on an emi- 
nence, but may be found anywhere on the wrinkled surface of 
