284 CH^ETODERMATID^E. 



NEOMENIID^, Neomenia] PRONEOMENIID^E, Proneomenia, Solen- 

 opus, Rhopalomenia, Macellomenia ; DONDERSIID^E, Dondersia, My- 

 zomenia, Nematomenia ; PARAMENIID.E, Paramenia, Ismenia, Lepi- 

 domenia, Echinomenia. 



Thiele (Zeitsch. wiss. Zool., Iviii, 278) suggests splitting the Neo- 

 meniidse into two families: NEOMENIID^E to contain the genera 

 Proneomenia, Rhopalomenia, Pruvotia, Neomenia and Paramenia, 

 and MYZOMENIIDJE for Macellomenia, Dondersia, Myzomenia, Nema- 

 tomenia, Ismenia, Lepidomenia, and Echinomenia. The distinction 

 is based largely upon features of the cuticular layer. 



Family CHJETODERMATID^. 



Body elongated, vermiform, the mouth and cloaca terminal ; 

 head defined by a constriction ; body cylindrical, clothed with 

 spiculose cuticle all around, without a foot-groove ventrally. Two 

 well developed feather-like gills; genital openings separated, the 

 genital ducts also functioning as nephridia. Sexes separated; no 

 copulating organ. Radula reduced to a conical peg of conchiolin. 

 Mid-gut with a posteriorly lying blind sack acting as a liver. 



Genus CHCETODERMA Loven, 1845. 



Chcetoderma LOVEN, Ofversigt of Kungl. Vet. Akad. Forh., i, p. 

 116. Crystallophrysson MOBIUS, 1875. 



Characters those of the family. Spicules alike all around the 

 body, of needle-shaped and flat forms. 



Chcetoderma lives upon mud bottom, mainly at a depth of 20 to 

 40 meters. It burrows in the mud, so that the dredge must be 

 weighted to secure them. Wiren writes as follows of specimens 

 kept by him in an aquarium, the bottom of which was covered by 

 a layer of mud : 



"When they were not disturbed they remained throughout the 

 day almost motionless in a perpendicularly descending burrow, the 

 anterior end directed downwards, the posterior upwards. The upper 

 mouth of the burrow was completely closed by the wider bell-shaped 

 posterior end, so that from the surface one noticed only the up- 

 wardly directed points of the two red gills. 



" When the animal was disturbed by the approach of any object 

 to the gills, it instantly contracted and bored down several inches 

 with extraordinary swiftness. It effected this progress by alterna- 

 tive lengthening and contraction of its body. In this the ante- 



