45 



condition I observed them in (fig. i6). Their size was: long 0,26 — 0,28 mm., shortest diameter 

 about 0,1 mm. 



This species is represented by one specimen only. It was found attached to the e.xtremity 

 of spine of Diadenia saxatile (Linn.) collected by H. jNI. .S. "Siboga" at; 



Stat. 53. April 21 — 22. Depth up to 36 m. Bay of Nangamessi, Sumba. 



I was at the end of the description of the pedunculate Cirripedia collected b)' H.M.S. 

 "Siboga" when I received this small and very curious form. I consider it so v^xy interesting, 

 that, though it is represented by one specimen only, I describe it as a new species. This compels 

 me, however, to create for it a new genus also, as it is perfectly impossible to range the 

 species under one of the existing genera. I am sorry to say that in consequence of its being 

 represented by only one specimen, which is moreover slightly deteriorated, it has not been 

 possible to study this new form in such detail as could have been desirable. Having dissected 

 numerous and very small forms of Crrripedia, I think it hardly possible that I should mistake 

 another part for a mandible or should overlook a pair of cirri, but the very peculiar shape of 

 these parts in the present animal have, I must confess, given me great trouble. I should have 

 prefered, before publishing a description, to control the details of its structure with the aid of 

 a richer material — I have tried in vain, however, to procure such. 



The outer shape of the capitulum of this new form is much like that of Alcpas. I could 

 not study the muscles of the peduncle in order to see whether they run up from the peduncle 

 and .surround the capitulum — as is the case in Alepas — without quite destroying the type. 

 But I think it probable that there is correspondence in this regard also between the two genera. 

 In Alepas corniita the inner rami of the 5"^ and 6^'^ cirri are rudimentarj', as was discovered by 

 D.ARWiN, and in some other species of the same genus a similar inequality has been observed. 

 Gruvel calls this the atrophy of one of the rami ; the cirri of Microlcpas diadciiiac show this 

 atrophy in both rami and to a much greater extent! The cirri of Anelasma have, according 

 to D.VRWiN, a shapeless and rudimentary appearance, being quite spineless, and not articulated. 

 Yet their anterior faces are more or less distinctly lobed, so that prominent steps can "be 

 counted, manifestly representing so many segments", as D.\rwix says. Though the cirri of 

 Microlepas diadenia are furnished with long hairy bristles, they are in a much more rudimentary 

 condition than those of Anelasma. In the genus Gynmolepas, as described by Aurivillius, all 

 the cirri have the rami of the same length, composed of 7 segments only; these rami in all 

 the cirri are almost of the same length as their pedicels — whereas those of the 2""^— 6'^ pair 

 in all other Lepadids are longer than those of the first pair and as a rule twice as long as 

 their pedicels or even longer. Aurivillius compares his new genus with Anelasma and says 

 that a reduction of all the cirri has occurred in these two genera. There can be no doubt, 

 I think, that a much more considerable reduction has occurred in Microlcpas diademael 



The parts of the mouth show an analogous reduction. So far as I know, all pedunculate 

 Cirripedia have mandibles with at least two, as a rule three or four, in some genera more 



45 



