218 AETHUR 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 35 mm. long. I have hitherto been unable to 

 obtain specimens of the two last-mentioned species ; but, 

 thanks to the kindness of Professor E. 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. 



The External 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 difiicult 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 papillae, which, according to 

 Koren and Danielssen, are disposed in regular rows. The 

 nature of these organs, which correspond with the papillae 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 



