eer st 
PAPA 
General Remarks. This species, like several others of the genus Ba/anus, 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 am 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 vestculosus 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 pair, of the 
middle segments of the 4" cirrus (which in the present species is even repeated, though more 
feebly, on the cirri of the 5" 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 Lalanus, 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 alanus, was discussed by me under the head of the genus itself. 
7. Sectio: Patella-Balanus 
21. Balanus calceolus Ellis. Pl. XXII, fig. 19—25. 
DARWIN, CH., Monograph. The Balanidae, Verrucidae etc. 1854. p. 218, pl. III, fig. 3a—3e. 
This species is represented by a single specimen in the Siboga-collection. Its 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 (Pl. 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, @ 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 Darwiy’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 (Pl. XXII, 
fig. 6 and @) 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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