426 NATURAL HISTORY AND ANATOMY OF 



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 setse 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 

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

 North Pacific. Of Bonncllia two species are recorded, both 

 inhabitants of -the Mediterranean, as is also the only known 

 species of Stemaspis. 



The Thalassemia 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 rwpivm. 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 earthworm, and 

 named it Lumlricus thalassema, under which name he de- 

 scribes and figures it in his Spicilcgia Zoological Montagu 

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

 lassina mutatoria.^ At the same time he expressed his 

 belief that his animal was identical with that described by 

 Pallas, but supposed that the figure given by that illustrious 

 naturalist was incorrect. This, however, is not the case, the 

 figure of Pallas well representing the animal after preserva- 

 tion in spirits, in which state doubtless he had only an oppor- 

 tunity of seeing it. 



Of late it has been taken by Mr. Harvey at Teignmouth : 

 from his specimen our structural account is drawn up. Of its 

 external characters it need only be mentioned, additional to 



* Fuse. x. t. 1. f. 6. f LinncciDi Trans, vol. xi. p. 24, t. v. f. 2. 



