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pointed teeth ; maxillae with numerous spines beneath the notch ; third pair of cirri resembling 

 more those of the fourth than of the second pair. No caudal appendages. Species living in 

 deep water. 



I described, in my Report on the Cirripedia of the Challenger-Expedition \ two species 

 of Balanus {B. corolliformis and B. hirsutus), which were collected in deep water and which 

 differed in several important points from the hitherto known species of the genus. These 

 differences concerned partly the structure of the shell, and partly the animal's body. Since 

 this report was issued, Pilsbrv - pnblished descriptions of two other species (B. callisto- 

 derma and B. hockianus), and , he pointed out that they belonged to the same section of 

 the genus as the above-named species collected by the Challenger. The one (/>. callistodermd) 

 was found in Japan-waters, at a depth of 140 m., the other (B. hoekianus) in Behring Sea, 

 at a depth of 77.5 m. Although Pilsbry's description with regard to the structure of the mouth, 

 of the labrum especially, is incomplete, his species, to judge from the structure of the shell, 

 certainly belong also to the same section of the genus Balanus. 



I now propose to give to this section the rank of a separate genus and to give it the 

 name of Hexelasma. The Siboga-material furnished me with two other species of the same 

 group and all these species correspond in an essential point : the absence of radii and, so 

 far as my investigations show, in a second point: viz. the shape of the labrum. The structure 

 of the cirri of the 3" 1 pair; moreover, is different from that in Balanus \ altogether, the new 

 genus is so far a very natural one, as all the species seem closely allied in structure, in 

 general appearance, and in the habit of living in deeper water. The relation between my new 

 genus and Balanus seems to be further removed than that between Acasta and Balanus: 

 the absence of radii in the first place, the structure of the compartments in the second, disting- 

 uishing it sharply from the true species of Balanus. The diagnosis given by Darwin for the 

 latter genus, when it comes to the point, is not applicable to these new forms; therefore we 

 have to choose : either to extend that diagnosis, or to separate those forms from the old genus, 

 and to establish a new genus for them. I have chosen the latter way. Darwin, already in 1854, 

 spoke of the large extent of the genus Balanus — and we have now still greater right to speak 

 of that : if we look at the question from a practical point of view, what reason can there 

 be to enlarge such a genus by extending its diagnosis? The very peculiar structure of the 

 labrum and of the 3 rd pair of cirri, which characterizes these new forms, shows, moreover, that 

 the differences affect the body of the animal as well as its shell. 



With respect to the differences in the animal's body, there exists a certain resemblance 

 between the species of my new genus Hexelasma and those of Darwin's Sub-Family Chthamalinac. 

 The latter never have the labrum notched in the middle, and their third pair of cirri always 

 resembles much more closely in external structure the fourth than the second pair — exactly 

 as I found it in Hexelasma corolliforme and H. hirsutum, and as is shown in the description 

 of the two new Siboga-species. In three species of the Clithamalinae belonging to two genera, 

 there are, however, caudal appendages, and these are not found in Hexelasma. The corres- 



' Hoek, P. P. C, Challenger Report. 1883. 



- Pilsbry, H. A., Barnacles of Japan and Bering Sea. Bulletin Bureau of Fisheries. XXIX. (1909). 1911. 



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