ANNELIDA POLYCHAETA. 37 



NOTE X. 



CONTRIBUTIONS TOWARDS THE KNOWLEDGE 

 OF THE ANNELIDA POLYCHAETA. 



Dr. R. HORST. 



On Arenicola-sipecimens from the Gulf of Naples. 



(Plate 3). 



Some time ago a finely preserved collection of Anne- 

 lids was procured by our Museum from the Zoological 

 Station at Naples ; among them I observed some specimens 

 of Arenicola, which in their characters do not agree with 

 the species , hitherto known from the European coast. 

 Going over the litterature about this genus, I saw that 

 not only there reigns a good deal of confusion in the de- 

 scription of the different species , but that we want even 

 an accurate knowledge of the feature of the bristles and 

 branchiae of our European species. Almost all the authors 

 have given an erroneous account of the appearance of the 

 branchiae of the common A. marina] nevertheless Wil- 

 liams 2 ) in the year 1851 already stated: »they are com- 

 monly described as forming an arborescent tuft; the 

 division of the vessels is however regulated by a fixed prin- 

 ciple. When fully injected with blood , the vessels of each 

 branchia form a single plane etc." Even a superficial 

 examination is able to convince us of the correctness of 

 Williams' assertion, though his drawing is not very accu- 



1) For Part I see Vol. VIII, p. 157. 



2) On the British Annelida; Report of the British Association for 1851, 

 p. 195, pi. 4, fig. 13. 



Notes from the Leyden Museum, Vol. XI. 



