CIRRIPEDIA. 21 



length of nine inches, and in one case three and one-half inches in diameter. It is con- 

 sidered, both by the natives of the west coast of South America and the travellers 

 who have eaten it, a delicious article of food. 



Chelonobia is a flattened form which is usually found attached to turtles or 

 Crustacea in tropical seas, the tortoise-shell turtle almost invariably having several 

 attached to his carapax. Coronula, 

 with its three species, diademia (Fig. 

 27), regina, and balcenaris, always 

 occurs imbedded in the skin of whales, 

 a habitat which is shared by Tubici'n- 

 ella, while Xenobalanus affects the 

 shell of Tortoises and skin of Black- 

 fish. 



Of the Cirripeds the Thoracica 

 alone have been found fossil. The 



Lepadidae appeared first, Pollicipes, FIG. 27. Coronula diademia, one-third natural size. 



the oldest genus, appearing in the 



Lias, while the family attained its culmination in the Cretaceous Period. Verruca 

 appears in the Cretaceous, while the Balanidae belong to the Tertiary and Recent times, 

 Balanus occurring in the Eocene of Europe and America. Many species have been 

 described by Lea, Conrad, Morton, Holmes, and others from American strata, but from 

 the fact that the opercular valves are usually wanting, it becomes very difficult to rec- 

 ognize the affinities of the species mentioned. The geological history, the structure, 

 and the development as far as known all point to the idea that Pollicipes is the ances- 

 tral form of the Thoracica, and from it have developed on one side the rest of the 

 Lepadida3, and on the other the sessile Balanidae and Verrucidae. 



J. S. KlNGSLEY. 



