Structure of Paleozoic Barnacles. — Clarke. 141 
union, or very closely matched lines of overlap, are distinctly 
exposed. 
The relation of the terminal plate of the right side to the 
caudal plate is simple, the latter apparently lying partly 
within the concave interior of the former, sufficiently so to be 
overlapped by it at the dorsal edge, so that the plate does not 
appear in dorsal view. The demonstration of an axial caudal 
plate in Lepidocoleus and Strobilepis determines the fact, par¬ 
adoxically enough expressed, that these fossils certainly em¬ 
brace the so-called capitulum of the Thoracica. 
It is evident that in Lepidocoleus we have to do with a 
highly simple unmodified form of cirripede, and it is unneces¬ 
sary to debate whether the fossil represents the capitulum or 
the peduncle of living barnacles; as just observed, it undoub¬ 
tedly includes the former and we have the best reason for 
believing that it is the entire exoskeleton of the animal. The 
sharp, linear ventral edge where the thin margins of the 
plates come into apposition without any sort of union was 
unquestionably a line of voluntary dehiscence for the protru¬ 
sion of the appendages. There is no evidence that the 
animal was of parasitic habit and we believe in the propriety 
of the assumption that inasmuch as the same simple arrange¬ 
ment of the plates is continued throughout the extent of the 
body, save at the caudal extremity, these quite fully repre¬ 
sent the entire length of the animal. The body plates, taken 
at a side view when the' fossil is properly oriented, show a 
typical crustacean segmentation. However different this 
appearance may be from the actual condition arising from 
the fact that the body plates are unsymmetrically placed on 
the two sides, yet a priori evidence is very strong that these 
are but a slight departure from the primitive simple segmented 
somatic condition to the highly modified test division of the 
typical cirripede. 
It is true that there is no basis for these assumptions in 
the ontogeny of living Thoracica. In both Lepas and Balanus 
the nauplius after various moults passes directly into a short¬ 
lived Cypris-stage, thereupon becoming attached and at once 
assuming ephebic characters, but in forms so radically modi¬ 
fied as are these, some of the ontogenic steps have been 
hastened and the record abbreviated. Hence there is here no 
