398 BALANID^E. 



This genus and the three following, namely, Platylepas, 

 Tubicinella, and Xenobalanus, have very considerable claims 

 to be separated as a sub-family, as has been proposed by 

 Drs. Leach and Gray. Although in structure and habits 

 they are certainly closely related together ; yet only few 

 characters can be predicated of all four in common, — some 

 characters failing in one genus and some in another. All 

 four, how T ever, differ from the foregoing genera in the oper- 

 cular valves not being articulated together, being simply 

 united by tough horny membrane ; but Chelonobia makes 

 some approach in this respect. All four have the branchiae 

 composed of a double fold ; but this can hardly be con- 

 sidered a character of much weight, as may be inferred from 

 the remarks made on this subject at p. 153 of the Intro- 

 duction, where the differences of these four genera from the 

 other genera of the family are discussed at some length. 

 Altogether I have been led to conclude, though with much 

 hesitation, that these genera had better not be separated as 

 the sub-family of Coronulinse. 



Our present genus, Coronula, is closely related to Platy- 

 lepas, and likewise to Xenobalanus, though this latter 

 genus is so very different in external aspect that it might 

 easily be mistaken for a pedunculated Cirripede. Lamarck 

 and some other authors have placed the species of Chelo- 

 nobia under Coronula, but this has arisen, as explained 

 under that genus, from a misapprehension of their structure ; 

 the folded very thin walls in Coronula having been compared 

 with the radiating septa of the very thick walls in Chelo- 

 nobia. I may further add, that Coronula has been divided 

 into two genera by Ranzani, on palpably insufficient 

 grounds. 



General Appearance. — The three recent species of this 

 genus have a very handsome and striking appearance. The 

 shell is highly symmetrical, owing to the six compartments 

 being of the same size and having exactly the same outline. 

 The general shape is either depressed or, as expressed by 

 the name, like a crown. The walls are longitudinally and 

 slightly ribbed, owing, as we shall presently see, to their 

 wonderfully folded structure ; and the surface is marked by 

 very fine longitudinal stria*, crossed by finely beaded lines 



