id standing ol these seven sp< ■ im< ol which mi closer 

 abl) I" found i" I"- identical; but I wish only to j >« >in t <>ut that there is, 

 to admil .1 causal nexus between the simplified structure of the 

 of life of these forms. 



jroup ol more or less degenerated forms, i 



\» remain. Of the latter those species in which the valves have the 



pment and show the greatesl resemblance to the valves of the nearly 



and LepaSy are most likely t<> repn lie more original form. In 



ard the described bj me ^ D. resstlis, by Annandale as /). tenuivalvata and by 



/>. occlusa are the first to 1"- named: their scutum is rather broad, their tergum 



the triangular shape of the species ol Lepas and their carina is likewise broad. Ni \i come 



D. Warvricki Gray and those which are nearly related to it: D. Hoekt Stebbing, 



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



■ - the scutum is composed of a narrow occludent segment and a much wider basal 



lent which, as a rule, has a triangular shape. With the more or less developed and 1 



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



i s terminates in a rectangularly infiected disc ' extending over a good deal of the base 



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



natural ^rouj» of species in die genus Dichelaspis. It is quite 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 lor me to undertake. 



Which species should come next? To judge trom the form of the carina />. pellucida 

 Darwin would be nearly related to />. Warwicki Gray; to judge trom the form of the tergum 

 rthogonia would be the nearest relative of the latter species and I think it would Ik- very 

 difficult to decide which characteristic is the more important. Then- remain 12 species, all of 

 them with rather narrow valves lea\in^ a great deal of the capitulum uncovered. These can 

 easily be divided into three natural and distinct groups. /). orthogonia Darwin 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 11. M.S. "Siboga" in the Malay 

 Archipelago and to be described later belong. />. pellucida, which has the carina much like 

 that of l>. Warwicki, has the tergum of quite a different shape: like a battle-axe as Darwin 

 ribes it -. not only D. Grayi Darwin luit 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 ,;inic holds for IK Lowei Darwin, D. Darwini Filippi, D. neptuni Macdonald, 



rioa 'i( his species /'. <;/.//</ terminates in a fork. Should this reall) 

 \. liad at his di ecimen only and this specimen most probably has nut been di: 



1 think it is h.inllv 1 lie >hapc ol' the terminal pari of the carina 



iiinl part \'. really united by a disc-lil 



- to lic a Dichelaspis. I think it bclongs to the same 



i.S 



