38 ANNELIDA POLYCHAETA. 



rate. Indeed each branchia of the common lug-worm con- 

 sists of about 12 secundary branchiae, connected by a 

 membrane at their base and situated next to each other 

 in the same plane, like the divisions of a palmated leaf; 

 these secondary branchiae are not irregularly branched , 

 but possess a middle axis , furnished on each side with 3 

 or 4 tufts of filaments (fig. 2). 



If the number of those lateral tufts much increases , as 

 is to be observed in some species of Arenicola, and the 

 middle axis bears on each side, in stead of 4 , 12 or 

 more racemous tufts, the secondary branchiae resemble 

 a feather (fig. 6). Therefore a South-American species , 

 provided with such plumous branchiae , was named by 

 Liitken Pteroscolex, which he wishes to be considered as 

 a sub-genus of Arenicola *). However if we would retain 

 this name, as proposed by Levinsen 2 ), then also our A. 

 marina ought to be ranged in that sub-genus , because 

 there is only a gradual difference between the branchiae 

 of A. antillensis and marina. Claparède seems not to have 

 rightly understood Lütken's description ; otherwise he would 

 not have written 3 ): »toutes les branchies sont disposées 

 dans un même plan, comme les nervures d'une feuille, et 

 ne forment pas de buisson touffu. Ce caractère a été relevé 

 chez une Arénicole des Antilles par M. Lütken etc." 



Branchiae, which are really arborescent, are to be met 

 with in A. Grubii (fig. 12), probably also in A. branchia- 

 lis , Boeckii a. o. • in those species the branchiae are bran- 

 ching directly at their base, and no real secundary bran- 

 chiae or branchial leafs are formed. 



JLrenicota Cluparedi Levinsen (fig. 1 and 1ö). — 

 loc. cit. p. 137, note; Arenicola marina L. var. minor 

 Clprd. — loc. cit. p. 40, pi. XIX, fig. 3. 



1) En ny vestindisk Sandorm, Arenicola {Pteroscolew) antillensis Ltk. ; Vi- 

 densk. Meddelels. fra Naturh. Forening i Kjöbenhavn, 1864, p. 120. 



2) System. -geogr. Oversigt over de Nordiske Annulata, ibidem, 1883, p. 137. 



3) Les Annélides Chétopodes du Golfe de Naples, 2e Partie, p 41. 



Notes from tlie Leyden Museum, Vol. XI. 



