286 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



are so fragmentary as to preclude detailed comparison. 

 Besides the -points mentioned above as common to the 

 three limnivorons families, the Opheliidse and Areni- 

 colidse agree in the character of their nephridia and in 

 their non-ganglionated nerve-cord. The main points of 

 difference between them are (1) the shape of the body; 

 (2) the skin, which is not sculptured and sub-divided into 

 annuli in Opheliidee ; (3) there are no branched gills and 

 no hearts in Opheliidee ; (4) the parapodia, on many of 

 which, in Ophelia, there is a filamentous dorsal cirrus. 



On comparing the Arenicolidse and Maldanidse the 

 differences are again more obvious than the resemblances. 

 They agree in the general form of their parapodia, in the 

 small number of nephridia and gonads, and in the simple 

 brain and ventral nerve cord with uniform covering of 

 ganglion cells. They differ in habit, the Maldanidse 

 have few but long segments, they have no gills and no 

 otocysts, and the tail segment is specialised. The ali- 

 mentary canal of Maldanidse is simple and bears no 

 special glands, and there are no hearts. The genus 

 Branchiomaldane presents features some of which are 

 intermediate between these two families. 



The anatomy of the Chlorhsemidse is imperfectly 

 known, but there appear to be no points in which they 

 approach the Arenicolidse. The former family differs 

 from the latter in its setse, septa, nephridia, median heart, 

 the processes of the prostomiiim and the ganglionated 

 nerve-cord. The Sternaspidse are still further removed 

 from the Arenicolidse by the peculiar arrangement of their 

 gills and seta?, the presence of ventral shields, special 

 genital ducts, coiled alimentary canal and only a single 

 pair of nephridia. 



It may be concluded that the Arenicolidse form a 

 compact family clearly distinguished from the neigh- 



