370 THE ANNELIDA POLYCHAETA. 



aa. Prostomium with a small anterior median process; notocirrus of first parapodia rudimentary; 

 notopodial setae of the most posterior somites stout crochets arranged in transverse rows. 



Paecilochaetus Claparede. 



Synonymy of Genera. 



Disoma Oersted and Poecilochaetus Claparede, formerly included in the 

 Spionidae, were removed as a distinct family by Mesnil (Bull. sci. France 

 Belgique, 1897, 30, p. 97), a procedure that seems amply justified. The two 

 genera are clearly distinct and may be separated as indicated above. Since 

 Disoma Oersted is preoccupied by Disoma Ehrenberg (Polyg., 1844), it is here 

 replaced by Disomides and the family name is altered accordingly to Disomididae. 



Other spionid genera, Magelona, Polydora, and Nerine of the Magelonidae, 

 Polydoridae or Leucodoridae, and Nerinidae respectively have also been re- 

 garded as types of distinct families; but at present there seems no clear justifica- 

 tion for these families. 



CiRRATULIDAE. 



The body of these annelids is elongated and linear, consisting of short 

 somites which are numerous, sometimes exceeding three hundred and fifty. 

 They are generally small or moderate in size, but may be as much as 300 milli- 

 meters long. They undergo strong retraction in preservation, often contracting 

 to half their length. The color is nearly always uniform and some shade of 

 brown or green, but may be a brighter shade of red ; and occasionally the body is 

 colored in spots over a paler background, as in Cirratulus pundatus Grube. 

 The liquid or plasma of the blood is red, containing haemoglobin, this giving to 

 the lateral branchiae a similar tinge and resulting in a characteristic appearance 

 in these forms. 



The prostomium is distinct, but much reduced in size, and is always devoid 

 of appendages. Eyes present or absent; often present in young stages and 

 absent in adults. 



The mouth is ventral in position. The peristomium and two somites 

 succeeding it are achaetous. On one or more of the anterior somites there may 

 or may not be present dorsal tentacular cirri or large tentaculiform organs, 

 recalling those of Spionidae, either dorsal or ventral in position. 



Notopodial and neuropodial fascicles of setae are present, making the para- 

 podia technically biramous; but there are no traces whatsoever of setigerous 

 protuberances or of either dorsal or ventral cirri, the body in consequence 

 resembling that of lumbrinereids or of some oligochaetes. 



