116 



Arenicolidae 



clearly visible in each segment, those of the posterior branchial 

 region are short and do not approach the rnid-ventral line ; the distal 

 part of each crotchet has a form resembling that of a swan's head, 

 that is, the region just proximal to the rostrum of the crotchet has 



,-N.GR. 



Fig. 48. A. pusilla, from California. 

 Anterior end, dorsal aspect ; show- 

 ing the large and folded lateral 

 lobes of the prostomium. 



"V^>. X6 



Fig. 49. A. pusilla, from Atka Island. Anterior aspect, 

 showing the prostomium (PR.), with its large lateral 

 lobes, the nuchal groove (N.GR.), and the mouth (Mo.). 



a full, convex curvature, 1 and is proportionally larger than in any 

 other species ; five pairs of nephridia, which open on the fifth 2 to the 

 ninth segments ; several (four to sixteen) pairs of oesophageal glands, 

 the anterior fairly long and slender, the others shorter and more or 

 less pear-shaped ; septal pouches absent ; statocysts absent. 



HISTORICAL ACCOUNT AND E EM ARKS ON THE TYPE SPECIMEN. 

 The species Arenicola pusilla was founded by Quatrefages on a single 

 incomplete specimen from Coquimbo, Chile. The diagnosis " Annuli 

 ebranchiati 9. Branchiae magnae ramosissimae " the only infor- 

 mation given, was inadequate, and the position of this with regard 

 to other species of the genus was indeterminable until the writer 

 (1910) examined the type specimen. 



Claparede (p. 301) seems to have suspected that Neapolitan 

 examples of "A. marina" might be specifically distinct from North 

 Sea specimens. He noted that the former were much smaller and 

 that their gills were not bushy; but it is remarkable that, while 

 studying the blood-vessels and nephridia, he did not observe and 



1 This character is especially clear in specimens not more than about 

 100 mm. in length. 



2 Barely is a nephridium present opening on the fourth segment. 



