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THK VOYAliE OF 1J.M.S. < II A IXENI ; Kit. 



species. A close examination, however, brought to light that in most other respects the 

 Zamboanga specimens closely resembled the species as described by Darwin, and so I 

 determined to class them with that species. 



General appearance, colour, form of the shell, and structure of the compartments as 

 described by Darwin. Size smaller; the largest specimen Darwin observed was 45 mm. 

 in basal diameter, and the largest specimen from Zamboanga measures only 31 mm. The 

 scutum is much like that described by Darwin, but the tergum has, in the first place, 

 the scutal margin very coarsely toothed ; and in the second place, its articular ridge, 

 which, according to Darwin, is not prominent, is very prominent indeed, and therefore 

 resembles much more the same valve in Tetraclita radiata. I have figured this valve (PI. 

 XIII. fig. 34). I almost feel sure that Darwin, had he known the specimens collected at 

 Zamboanga, would have proposed only one species, instead of the two nearly related ones — 

 Tetraclita coerulescens, Spengler, sp., and Tetraclita radiata, de Blainville, sp. And it is 

 this consideration which has withheld me from describing the Challenger specimens as a 

 third distinct species. 



To one of the specimens a Balanus was attached, which was still young, and probably 

 belongs to one of the varieties of Balanus amphitrite, Darwin. The adductor ridge at the 

 internal side of the scutum, however, was not very distinctly developed. 



The specimens of Tetraclita coerulescens were taken at Zamboanga, October 23, 1874, 

 from a depth of 10 fathoms. 



Coromda, Lamarck, 1802. 



This genus comprises those sessile Cirripedia which have six compartments of equal 

 sizes, and thin, deeply folded walls, with the folds forming cavities open only on the 

 under side of the shell ; their opercular valves are much smaller than the orifice of the 

 shell. 



Of this genus Darwin knew three living species : Coronula balaenaris, Gnielin, sp., 

 attached to whales in the Southern Ocean ; Coronula diadema, Linn., sp., of the 

 Northern Atlantic Ocean; Coronula regina?, Darwin, attached to whales in the Pacific 

 Ocean. They may be distinguished from one another in the following way : — ■ 



Coronuhi. 



I. Ribs of the compartments flattened. 



1. Radii very thick, opercular valves four, 



2. Radii thin, terga absent, . 

 II. Ribs of the compartments convex, 



Coromda balaenaris, Gmelin, sp. 

 Coronula regincB, Darwin. 

 Coronnln diadema, Linn., sp. 



Coronuhi diadema is the only species which is represented in the collection made 



during the cruise of H.M.S. Challenger. 



