164 



course, species in deeper water may as well have developed from such forms: the species of 

 Balanus occurring in deeper water (see the table p. 153) do not belong to one and the 

 same section and, probably, had a very different descent. 



1. Sectio: Mega-Balanus 



1. Balanus iintinnalutlum (Linn.). 



Darwin, Ch., Monograph. Balanidae and Verrucidac. 1854, p. 194, pi. I. fig. a — /, pi. II, fig. \a — \o. 



This species is represented by one sample only : a few specimens, which were found 

 attached to the bottom of H. M. S. "Siboga", when the ship was docked on October i5 th , 

 1899. The ship had been previously docked and cleaned on June i st , of the same year : so the 

 Balani, probably, developed in the period between the two dates. 



The sample is composed of four specimens that caused me great trouble. One of the 

 specimens can be determined at once as belonging to Darwin's variety (3) valialus\ but the 

 remaining three represent two forms, not only different from the first, but also different from 

 all the varieties (11 in all) described by Darwin. Therefore the case mentioned by Darwin in 

 which three most distinct varieties were taken from the bottom of the same vessel, is here 

 repeated. The three specimens are relatively small, and I do not feel sure, therefore, that they 

 are full-grown animals. Their form — of one especially — is so characteristic, that I really prefer 

 to describe them as different varieties. 



a. B. tintinnabulum, var. validus Darwin. 



The specimen looks exactly like the figure (PI. I, fig. c) given in Darwin's Monograph. 

 The coarsest and strongest specimens that Darwin saw, were said to have been attached to 

 a surface of iron : this holcis good also for the one taken from the surface of the "Siboga"; 

 parts of the outer surface of the basis are coloured red, from the ship's being painted with red-lead. 



The shape of the shell is conical, slightly convex at the rostral side ; it is coarsely 

 ribbed, with some of the ribs flexuous and most of them rugged ; the orifice is relatively large, 

 rounded, angular, but at the rostral and carinal extremities, the basis is partly lost, the 

 remaining part is flat and the whole must have measured 29 and 20 mm. in diameter. The 

 tergum corresponds almost exactly to the figure given by Darwin for his variety communis: 

 it has a well-developed longitudinal furrow, which is quite closed, a prominent articular ridge, 

 extending over three fourths of the length of the valve, the spur is produced for a con- 

 siderable distance up the internal surface of the valve, the crests for the depressor muscle 

 are only feebly developed. The scutum has rather prominent lines of growth, the general 

 shape resembling that of Darwin's var. coccopoma. The articular ridge is broad, much reflexed 

 and slightly hooked at its base, it extends over half the length of the valve. The adductor 

 ridge is well-developed and the cavity for the lateral depressor muscle rather deep. 



Darwin did not say where his specimens of this variety were collected. We now know 

 for certain that it occurs in the Malay Archipelago. 



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