512 verrucid^:. 



that he once saw it adhering to tidal rocks and like- 

 wise to some floating bark. Generally the species are 

 attached to living organic bodies, especially shells of 

 Mollusca and of Cirripedes, to Gorgoniae, and Laminarias ; 

 less frequently to rocks. We shall immediately see that it 

 has slight powers of excavation. This genus is geologically 

 older than any true sessile cirripede or member of the 

 Balanidae : V. Stromia is found in the Glacial Deposits and 

 in the Red and Coralline Crag of England : another species 

 (in a state not to be identified) occurs in the ancient Tertiary 

 formations of Patagonia ; and another in the Chalk of 

 England and Belgium. The fact of this Family ascending 

 to a Secondary epoch accords, in an interesting manner, 

 with its affinities ; inasmuch as though in appearance a 

 sessile cirripede, it is almost equally related to the Lepa- 

 didae and Balanidae, and is more nearly related to the 

 Lepadidae than to the Balaninae, or typical members of the 

 Balanidae : of the latter, none have hitherto been found in 

 any Secondary deposit, whereas the Lepadidae culminated 

 during the Cretacean period. 



Powers of Excavation. 



My attention was called to this subject by Mr. Hancock, 

 whose excellent researches on the boring of Mollusca are 

 well known. Verruca Stromia, when attached to shells 

 destitute of an epidermis, excavates, as he informed me, a 

 slight depression, deepest in the middle ; but when the 

 epidermis is present no effect whatever is produced. We 

 shall presently see that the central depression is in some 

 degree distinct from that of the circumference. I have 

 since found Mr. Hancock's observations strictly applicable 

 to V. laevigata, V. Spetigleri, and to an ancient tertiary 

 species from Patagonia. From having found that the 

 following cirripedes, viz., Lithotrya, Alcippe, and Crypto- 

 phialus, all form their deep excavations by mechanical 

 means, and from having read the above-mentioned memoirs 

 by Mr. Hancock on the boring of mollusca, I was strongly 

 impressed with the idea that the action in Verruca would 

 likewise prove mechanical : but from the following facts I 



