:h in a single r<>\\ ; they are always by far the strongesi pair of parts in the 



about doublé the size of the maxillae. Now the mandibles of MicroUpas 



ili whatever, the inferior angle only hein- furnished with a somewhat 



spine than those which are planted along the free edge; further, the mandible <>f tliis 



c'irr; i hardly be said to be larger than the maxilla. The latter in all other Cirripedia 



al the upper corner and numerous more or less strong spines along the edge: 



in .1. diademae it has the edge regularly curved and furnished with several rows of 



delicate hairs its inferior angle showing a slightly stronger spine-like hair, an other 



being inserted at a little distance from that angle. 



I'hc extremely rudimentary condition of the lïrst pair <>f cirri and the fact that caudal 

 appendaj wanting complete the description of a pedunculate Cirriped, which so far ;is 



structure of the body with its articulate limbs is concerned, must be considered as one of 

 the most reduced at present known. This reduction concerns the body of the little anima! only — 

 capitulum gives at least the impression of being that of an ordinary Alepas. It is of course 

 very difficult to understand how such an exceptional reduction has taken place and the circum- 

 stance that I am quite ignorant of the mode of life of Diadema saxatile makes it perfectly 

 hopeless to seek for an explanation. I do not know, for instance, what position the club-shaped 

 spine, at the tip of which our Microlepas was placed, occupies on the body of the Echinid, 

 whether this spine is highly moveable etc. There is every reason to think, that the reduction 

 of the limbs, parts of the mouth and cirri, is in accordance with the nature of the food and the 

 way in which this is grasped by the little animal — I do not know, however, what ditïerence 

 there is between its prey and that of other Cirripedia. We are therefore unable to explain the 

 physiological side of the phenomenon; its morphological importance lies in the high degree of 

 reduction and in the fact. that — so far at least as our present knowledge goes — no real 

 intermediate forms can be said to occur which could bridge over the gap between an ordinary 

 Alepas and this cripple-like form. 



Genus Ibla Leach 



The Cirripeds of the genus Ibla are characterized by the absence of calcareous matter 



in the valves and spines of the peduncle, by the presence of four valves (two scuta and two 



also by the fact that (in the one of the known species) the sexes are separated, or 



that (in the other species) the "masculine efficiency is aided by one <>r two complemental 



male. 1 >\k\\i\ . 



Of this genus two species were known to Darwin in 1851. Since that year no new 

 species have been described, nor have the original s|)ecies of Darwin been often met with. In 

 his list of 1897 Wei 1 nf.r ' mentions the occurrence of Ibla Cumingi Darwin in the Red Sea, 

 in the neighbourhood of the Philippines and al Zamboanga (also Philippines), and of Ibla quadri- 

 valvis (Cuvier) at Van Diemensland. Of the latter species Grüvel 9 found numerous specimens 



1 Um . u .. Verzeichois u. s. w. Archiv f. Natu: 1897 Bd I. 



Cirripides appartcnant a la collection du Muséum d'histoire naturelle. Nouv. archiv. du Mn 



,03. 



46 



