370 Messrs Forbes and Goodsir on the Natural History 



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 Sipunculacea*, which have a tentacu- 

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

 its base ; and from the Priapulacece which have a trunk without 

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

 extremity at the end of a long filamentose caudal appen- 

 dage, which has been regarded by some naturalists as a respi- 

 ratory organ. 



The genera Thalassema, Echiurus, Bonellia, and Sternaspis, 

 constitute the family. The first has a simple oral appendage 

 and no corneous bristles surrounding its anus ; the second has 

 also a simple oral appendage, but has circles of corneous 

 bristles or seta; surrounding the posterior extremity ; the third 

 is distinguished by its forked oral appendage ; and the fourth 

 is marked out from its allies by the possession of a corneous 

 disk, surrounded by setae placed near its anterior extremity. 

 But few species are included in these four genera. Of Tha- 

 lassema but one is known. Of Echiurus two have been de- 

 scribed, the one a native of our own seas, the other of the 

 North Pacific. Of Bonnellia two species are recorded, both 

 inhabitants of the Mediterranean, as is also the only known 

 species of Sternaspis. 



The Thalassema Neptuni is a native of the coast of Corn- 

 wall and Devon, where it lives among submarine rocks. 

 Hence Lamarck, in the first sketch of his history of Inverte- 

 brate Animals, styled it Thalassema rupium. It was discovered 

 by the observant Gaertner, and by him sent to Pallas under 

 the name by which it is now known. Pallas, however, con- 

 sidered it an annelide, and an ally of the earth-worm, and 

 named it Lumbricus Thalassema, under which name he de- 

 scribes and figures it in his Spicilegia Zoologica.* Montagu 

 afterwards found it and described it under the name of Tha- 

 lassina mutatoria.f At the same time lie expressed his be- 



* Fasc. x. t. 1. f. 6. f Linnaeau Trans, vol. xi. p. 24. t. v. f. 2. 



