INTRODUCTION. 5 
The existence of a Cretaceous Verruca is an apparent exception to the rule, as this genus has 
hitherto always been ranked among Sessile Cirripedes ; but Verruca, as we now know, must 
be placed in a family by itself, namely, the Verrucide, quite distinct from the Balanide. 
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 that section of the genus, which has the walls and 
basis permeated by pores. Generally, the extinct forms belong to the section, 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 Chthamalinz approach much more closely than do the Balanine 
to the ancient Lepadide, 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 larger than on this side of the Atlantic. 
I already have given my reasons for very seldom naming any Sessile Cirripede 
without examining the opercular valves: it has been owing to this, as it appears to me, . 
proper want of caution, that there are so many nominal species. Thus it is made to 
appear in catalogues, that the tertiary seas abounded with species of Balanus to an 
extent now quite unparalleled in any quarter of the world. Bronn,’ for instance, in his 
invaluable ‘Index Palzontologicus,’ gives the names of thirty-five Balani, found fossil in 
Europe, and I have not counted those found only in alluvial deposits, as they would 
certainly be the same as the still living species. Now I know only eleven recent Balani 
on the shores of all Europe, from the North Pole to lat. 30°; and of these I doubt whether 
B. balanoides and improvisus have been found fossil. In the Red Crag there is one extinct 
Balanus: in the Coralline Crag, which seems to have been very favorable to the existence 
of Cirripedes, there are six species of Balani, of which two are absolutely extinct, and 
one does not occur in any neighbouring sea: in the Hocene formations the species seem 
to have been rare, and I have seen only one, and that is an extinct form. ‘Taking these 
several facts into consideration, and bearing in mind that Cirripedes usually range widely, 
| To save any other person interested in fossil Cirripedia, going through the several works quoted by 
Bronn, I have given some remarks on his list of species, in an appendix at the end of the Balanide, in my 
volume published by the Ray Society. 
