414 BALANIDiE. 



specimens, of the size of a shilling, the entire shell, with the 

 exception of the operculum, is thus covered up and pro- 

 tected whilst young and tender. 



Geographical Distribution. — The genus is found wherever 

 whales occur, that is, from the Arctic to the Equatorial 

 regions, in both hemispheres. It is asserted that sometimes 

 as many as a couple of hundred specimens will adhere to a 

 single whale. Coronula barbara, a form closely allied to 

 C. diadema, existed during the Red Crag period ; and 

 Bronn has described some fossil specimens from Italy. 



Affinities. — In the wonderfully convoluted shell, — in the 

 parietal tubes not being either filled up by calcareous layers 

 or being crossed by calcareous septa, — in the outer lamina of 

 the shell between the longitudinal septa near the basis being 

 imperfect, Coronula differs from all the foregoing genera ; in 

 the two latter respects it agrees with the three following 

 allied genera, viz., Platylepas, Tubicinella, and Xenobalanus. 

 The equal size of all six compartments of the shell, has been 

 observed in very few genera besides Coronula. In a new 

 opercular membrane not being formed at each exuviation, and 

 in two or three of these membranes being persistent, and in 

 their being attached high up the sheath, this genus agrees 

 with the three following genera alone. In the valves tending 

 to be rudimentary, and in the protuberant lips of the sack- 

 aperture, we have a close alliance with Xenobalanus. The 

 muscles of the sack being spread out, and tending to lose 

 their transversely striated character, are great peculiarities in 

 Coronula, Tubicinella, and Xenobalanus. The simplicity 

 of the cement-ducts is a remarkable character, observed in 

 two of the following genera, but not in Tubicinella. The 

 double branchiae is a peculiarity common to all four genera. 

 Neither the mouth nor cirri offer any new characters of 

 much importance in Coronula or in the three allied genera : 

 the lower teeth of the mandibles not being laterally double, 

 but having small intermediate teeth, is the newest feature 

 in the mouth. 



