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Darwix's Sc. villosiiin, like 5^. trispinosum collected by the "Challenger" and like Sc. pollici- 

 pedoides taken by the "Siboga", have a simply keeled, relatively short and nearly straight 

 carina, a sub-carina and a rostrum. The shape of the valves in these species, of the lower whorl 

 especially, is triangular with the umbo at the apex, i. e. at the extremity opposite to the peduncle. 

 Darwin said (in 1S51), that Sc. villosum "leads on to Pollicipes"; I think he would quite agree 

 now that we had better consider that species and those nearly related as derived from Pollicipes. 

 The form of the valves, their number, the occurrence of a sub-rostrum in Sc. villosum (as in 

 the no doubt nearly related Sc. calyculus Aurivillius) the occurrence of two extra valves of the 

 lower whorl in one of the specimens of Sc. pollicipedoides , mihi (cf. the description of that 

 species in the present report) are I think so many proofs for the correctness of that theory. 



The other forms are considered by me to be derived from the species with a simply 

 keeled, straight carina. I think w^e ought to divide them into three groups which I suppose 

 developed independently from the forms with straight carinae. Calling the place where the umbo 

 is situated in a species like Sc. villosum its upper extremity, we see the carina lose its original, 

 straight form either by adding almost equally at both ends, in which case its shape becomes 

 angularly bent; or by growing exclusively downwards, its shape becoming more or less strongly 

 bowed and its umbo remaining at the apex; or, in the third place, by doing both, that is 

 adding at both ends, but much more .strongly downwards and assuming- at the same time the 

 distinctly bow-ed shape of the carinae of those species which have this valve simply bowed and 

 not angularly bent. 



From the presence of a sub-carina in most and of a rostrum in all I conclude that the 

 species with an angularly bent carina are slightly more primitive than those with a bowed carina. 

 The latter never have a sub-carina and in many a rostrum is also wanting '. The structure of 

 the complemental males shows also that the species with an angularly bent carina are more 

 like the primitive Scalpellums than those with a bowed carina. Between the two main groups 

 I place those species in which the carina has an intermediate structure. To this last group 

 belong most of the species for which I proposed, in my report of 18S3, to create the division 

 distinguished by imperfectly calcified valves. 



We would thus have the following four main divisions : 

 A. Species in which the carina is nearly straight with the umbonal part as 

 a rule projecting freely; a sub-carina and a rostrum are present. Valves 

 of the lower w-horl triangular, with the umbo at the apex. The little 

 males, so far as known, have a capitulum with distinct valves. [Sectio: Proto-Sialpclluni\ 



Number of species of this group at present known: 14. It is represented 

 in the collection of the "Siboga" by three species : Sc. pollicipedoides n. sp., 

 Sc. aries n. sp. and Sc. aciitum Hoek. 



1 With regavd to this valve I wish to point out the following difficulty; originally it always belongs to the valves of the 

 capitulum, but in several species it is overgrown or covered by the rostral lateral, the rostral margins of the right and left valves touching 

 one another in the medial line. Sometimes these margins are slightly hollowed out in the middle, in which case a narrow oval-shaped 

 area is seen at tlie place where the rostrum should be ; in that case it is very difficult to decide whether a rostrum is present or not 

 without preparing and isolating the valves — and it is, of course, better not to do so in all those cases in which a species is represented 

 by only one specimen. The value of the rostrum for classification purposes is diminished by this circumstance. 



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