NATURAL HISTORY AND ANATOMY OF THALASSEMIA, ETC. 425 



XL— ON THE NATUEAL HISTOEY AND ANATOMY 

 OF THALASSEMA AND ECHIUEUS. By Edward 

 Forbes and John Goodsir* 



Among the Eadiata of the British seas are two animals which, 

 in their general appearance, rather resemble Annelides than 

 Ecliinodcrmata, to which latter class they structurally belong. 

 These are the Thalassemia neptuni and Echiurus vulgaris, 

 members of the family Tlialasscmaccai in the order Sipunculidce, 

 a zoological and anatomical description of which species we 

 have to-day the pleasure of submitting to the "Wernerian 

 Society. 



The family Thalassemacece includes a group of vermigrade 

 Ecliinodcrmata, characterised by having cylindrical worm- 

 like bodies terminated at one extremity by a mouth, which is 

 placed at the end of a short proboscis, to which is appended a 

 remarkable sheath-like appendage, and at the other by an anus 

 with no external appendages. 



These characters distinguish it from the other families of 

 its order ; from the Sipunculacece, which have a tentaculated 

 trunk, no sheath-like appendage, and an anus placed at its 

 base ; and from the Pricqndacca;, which have a trunk without 

 tentacula, no oral appendage, and the anus at the posterior 

 extremity at the end of a long filamentous caudal appendage, 

 which lias been regarded by some naturalists as a respiratory 



organ. 



The genera Thala wema, Echiurus, Bonnellia, and Stemaspis, 

 ' Read before the Wernerian Natural History Society on 23d January 



!- II. 



