74 Mr. T. H. Withers on 
Carina.—This valve is of the same length as the carinal- 
latus and the apices of these two valves, together with that 
of the tergum, form the upper extremity of the capitulum. 
The valve is narrow, almost linear, nearly flat, about the 
width of the carinal plates of the peduncle, and there is a 
corresponding valve on the opposing side of the capitulum. 
Wyville Thomson has written in his description of S. mac- 
adami—“ ... . this valve must be either one of the valves of a 
split carina—one of the parietes of a carina in which the 
tectum is undeveloped; or we must suppose the carina to 
have been composed of two parietes and a separate tectum, 
and the tectum to have been lost.”’ In my opinion it is one 
of the halves of a split carina in which parietes or intra- 
parietes had not been developed, and the valve is of the 
same type of structure in S. pulchellum and S. haworthi. 
A ridge is invariably formed along the median line in the 
carinal valves of ordinary pedunculate cirripedes, and a 
modification such as the splitting along this line would not 
be unexpected. Such a secondary modification is seen in 
the splitting of the dorsal plate in certain species of the 
recent Molluscan genus Pholas. While such a modification 
of the carina is quite unique among fossil and recent cirri- 
pedes, a somewhat similar modification in the scutum is seen 
in certain species of the recent genus Pecilasma. The scutum 
in that genus, as in the closely allied genus Lepas, has the 
umbo situated at the rostral angle, and the growth is entirely 
upwards. In Lepas a ridge is formed on the scutum ex- 
tending from the umbo to the upper extremity of the valve, 
and running near and almost parallel to the occludent 
margin. Hssentially in the same position as the ridge in 
Lepas, a suture is formed, which can be observed on both 
‘surfaces of the valve in one speces of Pecilasma, The 
development is carried a step further in other species of that 
genus, for in those the scutum is definitely split into two 
pieces. 
Peduncle.—This is about three times the length of the 
capitulum, and in its upper part, just below the line of 
junction, it is rather wider than the capitulum. It is com- 
posed of ten rows of smooth calcareous scales, five on each 
side, forming a most beautiful loricated structure, sharply 
pointed at its lower extremity. There are as many as twenty- 
seven scales in a row in one of the specimens from Kansas, 
but the number naturally depends on the size and age of 
the individuals (see immature example depicted on PI. IV. 
fig. 1 A). The summit of the peduncle is usually somewhat 
obliquely truncated, being lowest at the rostral end ; this is 
