Darwin's s like Sc. trispinosutn collected by the " Challenger" and like Sc. pollici- 



the *Siboga", have .1 simply keeled, relatively shorl and nearly straight 



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



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



D l (in 1851), that Sc. villosum "leads on to Pollicipes"; I think he would quite a 



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



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



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



lower whorl in one ol the specimens of Sc. pollicipedoicles, mihi cf. the description oi that 



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 



d, straight carina. I think we ought to divide them into three groups which I suppose 



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



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



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



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 bowed 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 niy report of 1883, to create the division 

 distinguished by imperfectly calcified valves. 



We would thus have the following four main divisions : 

 . /. 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 

 <>f the lower whorl triangular, with the umbo at the apex. The little 

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



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. acutum Hoek. 



1 With regard to this valve I wish to point out the following difficulty; ■ t i^inally it always bclongs to the valves of the 



1 by the rostral lntcr.il, the rostral margins of the right and left valves touching 

 l line. S imetimi are slightly hol to wed out in the middle, in which rrow oval-shaped 



• til jdacc where the rostrum should 1»-: in that C« whethef a rostrum is present i 



•ing the valves — and it is, of course, hetter not to do so in all lh< in which a species is repri 



Uic of the rostrum f i'.n purposes i- diminished by this circunistance. 



5» 



