Arcnicola pusilla 117 



comment upon the presence of several oesophageal glands. Dr. 

 Levinsen placed tlie Neapolitan specimens in a new species, " A. 

 Claparedi," distinguished from A. marina by the presence of pinnate 

 gills and by certain cliaetal character.^/ which, however, are valueless 

 for specific discrimination. As pinnate gills occur in some specimens 

 of A. marina this character does not serve to differentiate Dr, 

 Levinsen's species. Under these circumstances it is not surprising 

 that many years elapsed ])ef()re this species was accepted generally. 

 It was, in fact, not until examination had shown that the internal 

 organs depart very markedly from those of A. marina that Dr. 

 Levinsen's species could be regarded as definitely established. 



Dr. Horst made a careful study of the gills and cliaetae ; Prof. 

 Elders described the external features of the anterior end, and 

 demonstrated the absence of statocysts - — the most remarkable 

 character of this species ; Prof. Fauvel gave a general description 

 of the internal organs, and Drs. Gamble and Ash worth a more 

 detailed account of the species, recording the first extra-Neapolitan 

 specimen. 



The Mriter (1910) has made an exhaustive examination of the 

 type specimen of A. pusilla, which is about 35 mm. long and 3 mm. 

 in diameter, and is incomplete, only 

 the anterior region, as far Ijack as 

 the eleventh chaetiferous segment, 

 being preserved. The first gill is 

 borne on the eighth segment, not 

 on the tenth as stated by Quatre- 

 fages, but is small. The neuropodia 

 of the branchial region are of the I . 



short type, and the crotchets ^^^^' 



/r.- r. I rr,N , t ii i'ig. 50.— A. ptisUlo. Type specimen, ri-ht 



(big. 24 B, p. DO) present dlStallV aspect of the tenth chaetiferous segment. 



, , . ) 1 1 • i" Note the short, wide neiu-opodium (Nkur.). 



the lorm or a swan s head, previously 



found to be characteristic of A. claparedii. The prostomium 

 (Figs. 51, 52, p. 118) is very fully extended, bringing into view the 

 posterior median portion, which in most specimens is hidden in the 



• The footnote, which gives Dr. Levinsen's diagnosis of the species, is as 

 follows : " Den niiddelhavske Art, for hvilken jeg foreslaar Navnet A. Claparedi, 

 stemmer ovcrens med vor Art [i.e. A. marina] i, at Gjitllerne begynde paa 

 syvende b0rsteb£erende Ring og strsekke sig over 13 Kinge, men afviger fra den 

 ved folgende Karakterer : GjajUer, som kun i et nieget kort Stykke ere forbundne 

 ved Grunden, langstrakte, med 10 I'ar Grene ; liygb^rster nied niegct svagt 

 udviklede Haar, Bugbvu-ster med sta?rkere tilspidset, lidt afsat, Eudedeel." 



- Which, however, he believed were represented by a pair of crypts near the 

 origins of the metastomial grooves. 



