CIRRIPEDIA. 169 



at the end of a stem {peduncle) more or less 

 flexible, we see the sides principally composed of 

 two pairs of angular pieces, each pair placed face to 

 face, and opening a little down one edge, while a 

 keeled piece unites them along the opposite edge. 

 The upper pair of opening valves are the terga, 

 the lower pair the scuta, and the keeled piece 

 behind is the carina. A small valve at the lower 

 part of the front edge, between the scuta, is the 

 rostrum, and there is sometimes a second piece 

 below this, called the sub-rostrum. Other valves 

 around the lower part, or between the scuta and 

 the carina, are called latera, or lateral valves ; and 

 they are named rostral, carinal, upper, or median 

 latera, according to their position. Similar ad- 

 jectives, distinguishing the several margins of the 

 valves, as the rostral margin, &c, are given for 

 the same reason; and the margins of the scuta 

 and terga which border the opening are the occlu- 

 dent margins. The scuta and terga are called 

 opercular valves ; and are moveable when all the 

 other valves are immoveable, by means of powerful 

 muscles attached to their interior surface. 



The sessile or stalkless Barnacles, or Acorn- 

 shells (Balanidce), appear to differ much in the 

 formation of their shells from the Lepadidce, but 

 the diversity is produced by modification of the 

 same essential valves. The scuta and terga are 

 placed within the other valves (which are soldered, 

 as it were, into a conical shell), and move up and 

 down in the orifice. The cone itself is resolved 

 into valves, some of which are much more de- 

 veloped than in the stalked species. In a com- 

 pletely developed form, the valves of the cone are 

 eight in number, of which the one from which the 



