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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 39. 



species; at least two other externally similar species of Arenicola 

 have gills as highly developed as those of A. pusilla. The characters 

 given in the original diagnosis of the species A. pusilla, one of them 

 erroneous, the other insufficient, can not be held to establish it as a 

 valid species, nor is there any feature of the internal anatomy which 

 marks this specimen as unique. 



The most striking of the external features of A. pusilla is undoubt- 

 edly its prostomium, the high grade of development of the lateral 



lobes of which is par- 



M.GR. 



Fig. 5.— Anteeo- ventral view of 

 i the anterior end of a specimen 

 i of a. clapaeedh from crescent 

 f city, california. x6. for let- 

 tering see fig. 3. 



Fig. 6.— Dorsal view of 

 the anterior end of the 

 SAME specimen. X6. For 



LETTERING SEE FIG. 4. 



' ' alleled, among known 



species, only in A. 

 claparedii. Figs. 5 and 

 6 represent the ante- 

 rior end of a specimen 

 of A. claparedii from 

 Crescent City, Califor- 

 nia (Harvard Collec- 

 tion), which has a 

 prostomium of the same type as that of A. pusilla, although owing to 

 contraction in the oral region at the time of preservation the ventral 

 portions of the lateral lobes of the Californian specimen have been 

 brought nearer together and have unduly compressed the median lobe. 

 Nevertheless it is obvious that the Californian specimen and A. pusilla 

 have prostomia of an identical type, and that the latter specimen, 

 judged by its prostomium, is to be referred to the species A. claparedii. 

 This diagnosis is confirmed by the examination of the internal organs, 

 the results of which are given above (p. 15), particularly by the 

 absence of statocysts, which is a feature of special significance. The 

 only point of difference in regard to the internal organs between 

 A. pusilla and A. claparedii is that in the former there are six 

 pairs of nephridia and in the latter typically only five pairs, there 

 being usually no nephridium opening on the fourth segment. But 

 this sole difference is not important; certainly it is not one which 

 would justify the separation of two otherwise identical forms. The 

 two examples of A. claparedii from Puerto Montt (seep. 10) have also 

 six pairs of nephridia; this may be a character of the Chilean race of 

 the species. We may conclude that the specimen of A. pusilla de 

 Quatrefages is a fragment of a small example of A. claparedii Levin- 

 sen; had it been complete it would probably have been about 80 to 

 90 mm. in length, A more detailed account of ''^. pusilla" and dis- 

 cussion of its affinities will be found in a forthcoming paper, by the 

 present writer, in Annales des Sciences Naturelles, Zoologie, ser. 9, 

 vol. 10, Paris, 1910. 



In his account of the specimens of A. claparedii from Puget Sound 

 Johnson" states that "the only notable points of difference between 



o Proc. Boston Soc. Nat. Hist., vol. 29, p. 1901, p. 421. 



