18 FOSSIL CIRRIPEDIA. 
examine a large series of fossil specimens from the Coralline Crag of England, and others from 
northern Italy, from Portugal, and from the southern United States, I at once discovered 
that the form of the denticuli on the strize of the scuta was quite a worthless character,—that 
in young specimens the scuta were simply striated,—that the prominence of the adductor 
scutorum ridge and the depth of the cavity for the lateral depressor muscle varied much 
(as in the case of the recent specimens), owing apparently to the varying thickness of the 
valve,—that in the terga the spur varied considerably in length and breadth, the latter 
character being in part determined by the varying extent to which the edges of the longi- 
tudinal furrow are folded in,—and lastly, that in young specimens the basal end of the 
spur is much more abruptly truncated than in the old. Hence I was led to throw the 
three recent forms, originally considered by me as specifically distinct, into one species ; 
but I may repeat that this considerable variation in the prominence of the adductor ridge, 
and in the depth of the pit for the lateral depressor muscle—the pit in some cases 
becoming even tubular—is a very unusual circumstance. 
With respect to the fossil specimens from the above stated distant localities, I consider 
them as belonging to one species, though they vary considerably in several points of 
structure. When compared with the recent specimens, they differ from them in often 
attaining a considerably larger size; in the parietes being generally longitudinally ribbed, 
as in the case of the Coralline Crag specimen (Tab. I, fig. 4a), and in the radii often having 
more oblique summits. Some of the specimens from the United States, have strong 
rugged, depressed shells, frequently resembling, to a curious degree, Bal. porcatus. On 
the other hand, considering the many points of identity between the fossil and the recent 
specimens, I have concluded, without much doubt, that they ought all to be classed 
together. In the Coralline Crag specimens, the spur of the tergum (‘I'ab. I, fig. 4g) is 
unusually long and narrow; it is broader in the Italian specimens (40), and either short 
(44) or long in the United States specimens. he scuta of the Lisbon specimens are 
remarkable for the great prominence of the adductor ridge, and for the depth of the lateral 
depressor cavity, as in most, but not in all, of the Panamaspecimens. The opercular valves, 
however, of some of the specimens from all these several distant localities are identical 
with the recent ones from the coast of America. I have entered into the above parti- 
culars, on account of, in the first place, its offering an excellent example how hopeless 
it is in most cases to make out the species of this difficult genus without a large series 
of specimens; secondly, as showing how the characters alter with age; and thirdly, as a 
good instance of the amount of variation which seems especially to occur in most of the 
species which have very extensive ranges. 
Some of the pink-striped Panama varieties, though having a somewhat different aspect, 
can be distinguished from certain varieties of B. amphitrite only by their scuta being lon- 
gitudinally striated,—a character in this species variable in degree, and in most cases of 
very little value. Some of the other recent varieties, however, are sufficiently distinct from 
B. amphitrite ; and the great fossil Coralline Crag specimens, which stand at the opposite 

