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described the discovery of that specimen as an interesting case of reversion in a short note 

 published by the Amsterdam Academy of Science 1 . I quote from that paper the following: 



Looking over the six specimens of this new species, I was struck by finding that one of 

 the specimens, though in other regards similar to the other five, differed from them by having 

 in the lower whorl of valves two latera in addition to the three which all the specimens possess. 

 In fig. 9, PI. V s the left side of a normal, in fig. 10 the same side of the abnormal specimen 

 is represented. (At the right side only one of the adclitional valves is developed.) In fact, the 

 few small valves which according to Darwin were wanting in the lower whorl of Sc. villosum 

 to convert it into a Pollicipcs occur in one of the specimens of this new species. By calling it 

 a case of reversion I would indicate the high importance, which from an evolutionary point 

 of view I attach to this abnormality. We need not go so far as to consider this species as 

 representing exactly the "missing link" between the genera Pollicipes and Scalpellum, but I 

 think the case shows clearly that a form with more numerous calcareous plates in its capitulum 

 (like Pollicipes) is the older, the form with fewer (like Scalpellum) the younger one; moreover 

 that the Scalp e Hum -species with straight carinae, inhabitants of shallow water, must be considered 

 as the oldest, i. e. the species most resembling the primitive form of Scalpellum. 



2. Scalpellum aries n. sp. PI. V, fig. 12. 



Valves thirteen. Carina straight. Scutum and tergum large. Upper latus narrow, nearly 

 reachino- the peduncle. Valves of the lower whorl six : a large and prominent rostrum, two 

 small rostral latera of triangular shape, two narrow carinal latera and a rather strong triangular 

 sub-carina. 



This species is represented by a single specimen only. 



The shape of the capitulum is nearly quadrangular with a triangular apex, being 

 broadest at its lower extremity. The scuta, terga and carina are much larger than the other 

 valves, the upper latus is medium-sized and of the valves of the lower whorl the rostrum is 

 the only one that is strongly developed. All the valves stand rather close together and are 

 not covered by membrane. Their colour is red or reddish, parts of the carina, of the tergum 

 and the scutum only being quite white. 



Scutum oblong, breadth slightly less than half the length, with the upper triangular 

 portion produced and the apex projecting beyond the occludent margin of the tergum. The 

 occludent margin is slightly hollowed out, the lateral margin convex. 



Tergum large, oblong, elongate-ovate, bluntly pointed at the apex, forming a sharp 

 ansfle at the lower extremity. 



Carina straight with the apex neither directed forward, nor backward; with a laterally 

 bowed roof, gradually widening from the upper to the basal end, rather deeply concave. The 

 upper part of the roof is at some distance from the tergum, which distance grows broader 

 towards the apex, the interspace being filled up by triangular lateral parts. 



' K. Akademie v. Wetensch. te Amsterdam, Froceedings of the Sectioa of Sciences, VII, 1905, p. 90. 

 2 Of the present publication. 



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