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It is not my task to discuss the good standing- of these seven species, some of which on closer 

 examination might probably be found to be identical: but I wish only to point out that there is, 

 no doubt, sufficient reason to admit a causal nexus between the simplified structure of the 

 capitulum and the mode of life of these forms. 



Considering these seven species as a group of more or less degenerated forms, i8 (19) 

 species of typical Dichelaspis remain. Of the latter those species in which the valves have the 

 most complete development and show the greatest resemblance to the valves of the nearly- 

 related genera Poecilasma and Lepas, are most likely to represent the more original form. In 

 this regard the species described by me as D. scssilis, by Annandalk as D. tenuivalvata and by 

 Lanchester as D. occlusa are the first to be named: their scutum is rather broad, their tergum 

 has the triangular shape of the species of Lepas and their carina is likewise broad. Next come 

 the species D. Warwicki Gray and those which are nearly related to it : D. Hoeki Stebbing, 

 D. antiguae Stebbing, D. alata Auriv., D. Aurivillii Gruvel and D. equina Lanchester. In all 

 these species the scutum is composed of a narrow occludent segment and a much wider basal 

 segment which, as a rule, has a triangular shape. With the more or less developed and broad 

 tergum these valves cover a good deal of the surface of the capitulum. The carina of these 

 species terminates in a rectangularly inflected disc ^ extending over a good deal of the base 

 of the capitulum. These five species (with D. Forresti (Stebbing), six ") form together another 

 very natural group of species in the genus Dichelaspis. It is (]uite another question whether 

 all these forms are really distinct species — but this can only be made out by comparative 

 study of all the original specimens, which study is not for me to undertake. 



Which species should come next? To judge from the form of the carina D. pellucida 

 Darwin would be nearly related to D. Warwicki Gray; to judge from the form of the tergum 

 IJ. orthogonia would be the nearest relative of the latter species and I think it would be very 

 difficult to decide which characteristic is the more important. There remain 1 2 species, all of 

 them with rather narrow valves leaving a great deal of the capitulum uncovered. These can 

 easily be divided into three natural and distinct groups. D. orthogonia Dar^vin forms a group 

 of its own amongst the hitherto known species: it has a triangular tergum with three (four) 

 prominent ridges and the carina terminates downwards in a small crescent-shaped cup : it is to 

 this group of the genus that two of the forms collected by H. M. S. "Siboga" in the Malay 

 Archipelago and to be described later belong. D. peliucida, which has the carina much like 

 that of D. ll^arzuicki, has the tergum of quite a diff"erent shape: like a battle-axe as Darwin 

 describes it; not only D. Grayi Darwin but also D. lepadiformis Gruvel come very close to 

 D. pellucida and if they are indeed distinct species they really form together an extremely 

 natural group. 



The same holds good for D. Loivei Darwin, D. Darwini Filippi, D. nephmi Macdonald, 



1 According to AURIVILLIUS the cavina of his species D. a/ata terminates in a fork. Should this really be the case, this species 

 would form a serious exception. But A. had at his disposal one specimen only and this specimen most probably has not been dissected 



for the study of the carina. But without doing so, I think it is hardly possible to make out the shape of the terminal part of the carina 



I'erhaps he only had the impression that the terminal part was a fork, its two teeth being really united by a disc-like plater 



2 I think Gkuvkl is right in considering Steehing's Tiichelaspis Forresti to be a Dichelaspis. I think it belongs to the same 

 section of the genus as D. Warwicki. 



18 



