244 SIPUNCULIDJG. 



Annelicles. These characters have induced many great 

 naturalists to remove them altogether from the Radiata, 

 and place them among the Annelides. Regarding, how- 

 ever, structural characters as the main tests of affinity, 

 and form, adapted to locality, as characteristic of analogical 

 relations, I cannot agree with their views, and accordingly 

 include them in this work. At the same time, our know- 

 ledge of their structure and habits is confessedly small ; 

 and future discovery will probably throw new and at pre- 

 sent unanticipated light on their position in the animal 

 kingdom. The tide of research may wash up new forms, 

 the want of which to guide us in our comparisons prevents 

 our proposing the arrangements here given as more than 

 provisional. 



The British species may be grouped under three very 

 distinct families : 



The Sipunculace^e, having a retractile proboscis, at the 

 base of which the vent is placed, and round the extremity 

 of which is seen a circle of tentacula. 



The Priapulace^e, which have also a retractile proboscis, 

 but no tentacula, and which have the vent at the extremity 

 of a long filiform caudal appendage. 



The Thalassemace^e, which have a proboscis, having a 

 long fleshy appendage attached. They have no tentacula, 

 and their vent is placed at the posterior extremity. 



Generic characters in the first of these families depend 

 on the form of the tentacula ; in the last on the presence, 

 absence, and arrangement of corneous bristles on certain 

 parts of the body. Of the Priapulacese there is but one 

 genus known. Specific characters throughout the tribes 

 appear to depend on variations of the integument and on 

 proportions of parts. Colour would appear to be of little 

 or no value, except perhaps in the last family. 



