The worms of our seas and fresh waters—variously classified and arranged by those who have studied them—have commanded till quite recently but a very poor share of the attention of the working naturalist. The probable reasons of this circumstance are to be found in the retiring nature of these animals, and the comparative obscurity of the characters which separate them specifically and generically, as well as the difficulty of tracing their life-histories and anatomical development. We believe that we are not exaggerating the true state of the case when we say that there is not a single work extant, such as is available for other groups of animals, by which species of Annelida may be satisfactorily identified—even those occurring in such limited areas,as our own and neighbouring seas. The few systematic works which are to be had, of which the British Museum Catalogue published in 1865 may be taken as a specimen, are simply useless for the purposes of the present day, owing to insufficiency in details in both descriptions and figures. On the other hand, the work of M. Malmgren on the Annelids of the North Sea, and such descriptions of species and ample drawings as those of Kinberg* and Ehlers, † - are examples of the manner in which the Annelida should be treated ; and until we get such works from many different localities the synonymy must remain in its present shocking condition, very many species which bear the same name in France, England, Germany, and Scandinavia, being quite distinct, and those bearing different names being often identical.