Balanus tintinnabulum (1 to 5). nigrescens* decorus* trigonus (3 and 4). concavus (3 and 4). amphitrite (1 to 5). amaryllis (4). allium* vestitus* imperator* Acasta sulcata* glans* Tetraclita porosa (3 and 4). rosea (2). purpurascens* vitiata (4). radiata (4) and West Indies. Elminius plicatus* simplex* modestus* Chthamalus antennatus* Chamæsipho columna* and Pacific Ocean (?). Pachylasma aurantiacum* Catophragmus polymerus* Alepas tubulosa* Ibla quadrivalvis* Scalpellum Peronii* Pollicipes spinosus* sertus* Lithotrya cauta* Here we have 30 species, of which 21 are peculiar. _Geological History._ The ancient history of the Balanidæ is a brief one. No secondary species has hitherto been discovered; in my monograph on the fossil Lepadidæ[80] I have shown that the negative evidence in this case is of considerable value, and consequently that there is much reason to doubt whether any member of the family did exist before the Eocene period. The existence of a Cretaceous Verruca is an apparent exception to the rule, as this genus has hitherto always been ranked amongst sessile cirripedes; but Verruca, as we now know, must be placed in a family by itself, quite distinct from the Balanidæ. Balanus is the oldest genus as yet known; it first appeared in Europe and North America, during the deposition of the eocene beds; and was at that time, as far as our information at present serves, represented by very few species. In South America, one species of Balanus abounds in individuals in the ancient Patagonian tertiary formation. I have seen, in the British Museum, specimens, said to have come from the eocene nummulitic beds near the mouth of the Indus, belonging to the second section of the genus. Generally, the extinct forms belong to the last section of this genus, which has the parietes not permeated by pores. During the miocene and pliocene ages, sessile cirripedes abounded. No extinct genus in this family has hitherto been discovered. It is singular, that though the Chthamalinæ approach much more closely than do the Balaninæ to the ancient Lepadidæ, of which so many species have been found fossil even in the older Secondary formations, yet that only one species of one genus of this sub-family has been hitherto found in any deposit; and that species is the still existing _Pachylasma giganteum_, in the modern beds of Sicily. During the epoch of the Glacial deposits in Scandinavia, Scotland, and Canada, the still existing species seem to have abounded; and they attained larger average dimensions than the same species now do on the shores of Great Britain, or even on the shores of the northern United States, where the average size seems