221 



General Remarks. This species, like several others of the genus Balanus, caused 

 me great trouble, which was made greater by the scantiness of the material. I certainly would 

 not have given a name to the species, nor undertaken a description of it but for the very 

 special character of the species. I ara quite sure that it will be possible to recognise it with 

 the aid of the description given here, should it be found again. The shape and the structure 

 of the opercular valves, of the scutum especially, show some resemblance to the valves of 

 Darwin's variety vesiculosus of B. tintinnabulum : the scutum shows a single row of square 

 holes such as, according to Darwin, are seen arranged in two or more rows radiating 

 from the apex of the valve, on young specimens of the above-named variety. But this seems to 

 be a somewhat accidental resemblance, the structure of the animal's body and of the cirri 

 especially, being quite different. The very peculiar armature of the cirri of the 3 ld pair, of the 

 middle segments of the 4 th cirrus (which in the present species is even repeated, though more 

 feebly, on the cirri of the 5 th pair), which Darwin considered as characteristic for the genus 

 Acasta, and which has now been observed by other investigators and myself in several species 

 of Balanus, in no other species of this genus is so well-developed as in the present. The 

 question as to the importance of this peculiar structure for the arrangement of the species of 

 the genus Balanus, was discussed by me under the head of the genus itself. 



7. Sectio : Patella-Balanus 



21. Balanus calceolus Ellis. PI. XXII, fig. 19 — 25. 



DARWIN, Ch., Monograph. The Balanidae, Verrucidae etc. 1854. p. 218, pi. III, fig. ^a — y. 



This species is represented by a single specimen in the Siboga-collection. lts shape 

 and the structure of the opercular valves leave no doubt as to its really representing this 

 species. 



Darwin's diagnosis of this species is a very short one: parietes and basis porose; scutum 

 with the pit for the lateral depressor muscle small and deep. The description and the figures 

 he gives, however, are much more explicit-. 



The shell (PI. XXII, fig. 19) is elongate and attached to a small piece of a yellowish- 

 coloured stem which perhaps belongs to a species of Gorgonia. The longest diameter of 

 the basis is about 8.5 mm., the greatest height of the shell 4.5 mm. The colour of the 

 shell is dull white, the basal parts of the compartments however, are brownish-purple, longitu- 

 dinal stripes of that colour radiating in the direction of the orifice; the basal cup which 

 almost quite encloses the little stem is coloured white. 



With respect to the scutum (PI. XXII, fig. 20, a and c) I must point out that the 

 apical part is slightly produced and upturned, the occludent margin being somewhat hollowed 

 out. This is not seen in Darwin's figure. Nor is the pit for the lateral depressor muscle so 

 distinct in the Siboga-specimen, as, according to Darwin, it should be. The tergum (PI. XXII, 

 fig. ó and d) has the apex slightly more produced, but the shape of the spur, with its very 

 characteristic longitudinal crests extending as so many little teeth beyond the margin, is exactly 

 as in Darwin's description. 



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