24 .\nnals of the South African Museum. 



The absence of statocysts seemed to indicate the former species and 

 the presence of nephridiopores on the fifth to the ninth segments 

 supported this view. The specimen was therefore referred to the 

 species A. claparedii^ but in my note-book it was registered as 

 probably belonging to this species 1 together with the comment that 

 further material, in a better state of preservation, was required in 

 order to permit a satisfactory determination. 



When Professor Gilchrist's specimens from Liideritzbucht came 

 into my hands it was at once noticed that their prostomium was 

 identical with that of A. assimilis, and an internal examination 

 proved, among other things, the presence of statocysts close to the 

 brain. It immediately occurred to me that my diagnosis of 

 Professor von Marenzeller's specimen might be erroneous. This 

 diagnosis rested almost entirely on two points, namely, that 

 statocysts could not be found and that nephridial openings were 

 present only on the fifth to the ninth segments. The search for 

 statocysts in preserved material is seldom easy, but it was attended 

 with unusual difficulty in that specimen, which had been more than 

 twenty years in alcohol and was not in good condition, so that the 

 possibility of having overlooked these organs was fully realised. 

 The specimens recently examined from Liideritzbucht, undoubtedly 

 examples of A. assimilis var. affinis, are peculiar in that all have 

 their nephridial apertures in the fifth to the ninth segments, that is, 

 on the same segments as in A . claparedii, and not on the fourth to 

 the ninth segments, as is usual in examples of A. assimilis from 

 other parts of the world. Such a local variation was not foreseen 

 or allowed for. The finding of this variation, which renders the 

 number of nephridiopores unreliable as a distinguishing character 

 between A. claparedii and A. assimilis, indicated that my provisional 

 diagnosis, made two years ago, rested on a very insecure basis : it 

 depended entirely on whether the absence of statocysts could be 

 regarded as proved satisfactorily. In order to remove the un- 

 certainty I applied to Herr Begierungsrat Ganglbauer, Director of 



* Aslncorth, J. H., " Die Arenicoliden-Sammlung im Konigl. Zoologischen 

 Museum in Berlin," in : Mitt. Zool. Mus. Berlin, Bel. IV., p. 351, 1910. 



f When the examination was made the difference in the form.of the neuropodial 

 crotchets of A. claparedii and A. assimilis had not been fully recognised and shown 

 to be constant. During the past few months I have examined many series of sette 

 from both these species and have found that, especially in the case of small or 

 medium-sized specimens, the crotchets usually afford considerable help in 

 differentiating these two species. The crotchets of A. claparedii are dilated near 

 the distal end so as to resemble the head of a swan, whereas the crotchets of 

 A. assimilis do not exhibit such a dilatation. 



