REPORT ON THE CIRRIPEDIA. 1 63 



Coronula diadema, Linn., sp. 



Lepas diadema, Linnaeus, Systema Naturae, 1767. 

 Coronula diadema, Darwin, Balanidse, 1854, p. 117. 



This is a very common and very characteristic species, for which Darwin gives the 



following diagnosis : — the shell is crown-shaped, with Longitudinal convex ribs, having their 

 edges crenated ; the orifice is hexagonal ; the radii are moderately thick and very broad ; 

 the terga are absent or rudimentary. The Challenger collected a single set of specimens 

 when at Bermuda in April 1873. They are small specimens, the largest of the seven 

 having a diameter of only 24 mm. 



With regard to the geographical distribution of this species, Darwin, who knew only 

 four specimens with certain localities attached to them, suspected that it would only 

 occur in the northern seas, Coronula regince replacing it in the Pacific. I have not 

 been able to find out whether this opinion is universally admitted at present. I believe, 

 however, that it is somewhat erroneous. Darwin himself found in the British Museum a 

 specimen among some shells of Mollusca from New Zealand, but he does not attach 

 much importance to this single instance, as an animal procured from a floating whale in 

 the early part of a voyage might so easily be sent home with specimens subsequently 

 collected in another region. In the Royal Natural History Museum of the Netherlands at 

 Leyden, there is, however, a single specimen of this species labelled " v. Siebold, Japan,'' 

 and I think that we have no right to doubt the correctness of this label. This specimen 

 is, moreover, very interesting on account of its great size ; its basal diameter is 78 mm., 

 whereas the largest specimen that Darwin saw was only 2^ inches in diameter (63 '5 

 mm.). In 1881, the Dutch schooner " Willeni Barents" collected a specimen of this 

 species at Vardo, which has about the same dimensions as the specimen from Japan. 



Chthamalus, Ranzani, 1820. 



This genus comprises those sessile Cirripedia which have six compartments, a 

 membranous basis, which sometimes (Chthamalus hembeli, Conrad, sp.) is calcareous in 

 appearance, owing to the inflected parietes. It is the only genus of the Sub-Family of 

 Chthamalinse, Darwin, which was instituted for those Balanidse in which the rostrum has 

 ake but no radii, in which the rostro-lateral compartments are without alae on either side, 

 and which have no porous parietes. 



All the species of this genus seem to be littoral; at Leasl Darwin says that this 

 is the case with all the species of whose habits he knows anything, and I do not 

 believe that in this respect our knowledge has been increased since the publication of 

 his monoo-raph. Owing probably to their littoral habits, Darwin does not believe that any 

 species of the genus has hitherto been found fossil. "Whether these two facts stand really 



