'5« 



which have the radii narrow or absent (ƒ?. Jïosculus) or not developed at all (B. vcstitzts), and 

 that Darwin's section C contains also B. perforatits, which has the radii either not at all 

 developed, or extremely, or only moderately narrow. Gruvel's species might perhaps find a 

 place in the latter section, which contains those species of Balanus which have the parietes and 

 the basis permeated by pores, and the radii, if developed, not permeated. 



Returning to the species represented in the collection brought home by H. M. S. 

 "Siboga", I will not enter too much into details regarding my experience (and very great diffi- 

 culties) in dividing the new species into the different sections of the genus. In several instances 

 this was found to be quite impossible. But to go on as was done hitherto, and to create a 

 new section for every species that did not enter so well into one of the sections previously 

 proposed, seemed also unsatisfactory. The conclusion was that I adopted a somewhat new 

 classification of the species of this genus, but without departing more than necessary from the 

 original division as proposed by Darwin. I think this classification must speak for itself. I 

 only wish to add that as I was obliged to include some of the known species in other sections, 

 and as the limits of these sections had to undergo some changes in consequence, and a few 

 other sections were to be introduced and a few of the old ones to be cancelled, I have thoueht 

 it better, to avoid confusion, to designate these sections in future with special names, as I 

 did with those of the genus Scalpellum, instead of using the characters A, B, C, etc. as was 

 done by Darwin. 



The sections I wish to propose are the following : 



Section Mega-Balamts (corresponding with Darwin's section A) is so-called, because 

 it contains the largest forms of existing Balani. This section is represented in the Siboga- 

 material by one well-known species only, so I have nothing to remark with regard to it. 



Section Ortho-Balanits is a combination of Darwin's Sections C and D ; it contains 

 Balani having the parietes permeated by pores, the basis sometimes permeated and sometimes 

 not permeated, and the radii not permeated. Numerous species (Darwin knew 14 living sjDecies) 

 belong to this Section, which, however, in the Siboga collection is represented by few species 

 only: B. amfrhitritc Darwin in different varieties, B. alatus n. sp. from a depth of over 500 m., 

 and B. mïnutus from 80 m. To this section belongs B. trigonus Darwin, the third cirrus of 

 which, according to Krüger, is furnished with curious thorns ("merkwürdige Dornen") along 

 the anterior face 1 ) of the segments. These curved hook-like teeth, as Darwin called them and 

 which he thought were peculiar to Acasta, are present also on the third cirrus of B. ampJii- 

 trite, B. alatus, and B. minutus. None of the species of Darwin's Section D are found in the 

 Siboga-collection. I venture to propose to include it with Section C in my Section Ortho-Balanus, 

 being of the opinion that the porosity or non-porosity of the basis is not of sufficiënt impor- 

 tance for separating these two sections. As Darwin pointed out himself, some species of Section 

 C (B. improvisus, B. lutbihts of the living species) have the basis imperfectly porose, whereas 

 a species of Section D (B. patel laris) has the basis "sometimes permeated by imperfect pores". 



1 KRÜGER also compares them — and of course he is right there — with ihe spines observed in Acasta; I do not quite 

 understand. however, how he can say that they are found on the dorsal side („auf der Rückseite") of the segments. They are in all the 

 species on the inner, anterior face of the segments. 



3° 



