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(full-grown and young) in the collection of the Paris Natural History Museum : they were from 

 "Port du Roi Georges" (King George Sound, West-Australia?), from Djibouti, from the east- 

 coast of Madagascar and from Mascatte. In both papers published by Gruvel j he treats the 

 o-enus Ibla rather extensively, but any newer literature on this genus seems not to be known 

 to him either. 



During the cruise of H. M. S. "Siboga" specimens of /^/«-species were collected at 

 different places in the Malay Archipelago. They belong to two different species : I. Cumingi 

 and another which is different from the two known from Darwin's Monograph. It comes near 

 to I Cumingi and is unisexual like that species; like both hitherto known species it is a 

 true littoral form. All the specimens collected by the "Siboga" were met with during reef- or 

 shore-exploration. 



To distinguish the species I give the following table : 



Ibla 



i. Hermaphrodite with complemental male (or males) /. quadrivalvis (Cuvier). 



2. Unisexual with dwarfed males. 



a. Yalves of the female coloured blue along the lateral margins 



and on the upper interior surface I. Cumingi Darwin. 



b. Valves without blue margins /. sibogae n. sp. 



i. Ibla Cumingi Darwin. 



Darwin found the specimens of this species "invariably attached to the peduncle of Polli- 

 cipes mitella, in groups of two or three together". The "Siboga" collected Pollicipes mitella 

 on two different occasions : at Labuan Badjo (Flores) and in the southern part of Molo Strait. 

 Ibla Cumingi was found attached to two of the specimens from the latter place. 



The specimens are not very numerous, nor are they very large. They not only show 

 the blue margins of the valves, but the structure of the body, of the parts of the mouth, the 

 cirri and the caudal appendages corresponds with Darwin's description. 



In the collections made during the "Siboga's" cruise there is another group of specimens 

 which I consider belong also to this species. They were taken however from the reef in Palos- 

 Bay, Celebes, and were not found attached to the peduncle of Pollicipes mitella. Their valves 

 have blue margins and the structure of the parts of the mouth and of the limbs is much the 

 same as in the specimens found at Labuan Badjo. 



( Weltner (1. c.) mentions the occurrence of this species in the Red Sea ; as Pollicipes 

 mitella is not known to occur there, this seems to be another instance of this species not living 

 "invariably" attached to the other Cirriped.) 



In all the specimens I dissected I found, at the place indicated by Darwin, a little male. 

 Darwin's description of these males is detailed and on the whole correct so I need not repeat 

 it here. A full description of the (complemental) males of Ibla quadrivalvis is given moreover 



Gruvei., A., Civnpèdes des expéditions scientifiques du "Travailleur" et du "Talisman". Paris, 1902. 



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