INTRODUCTION. 



On the Names given to the different parts of Cirripedes. 



In my former volume I stated that I had found it indispensable, in part owing to 

 the extreme confusion of the nomenclature previously used, to attach new names to several 

 of the external parts of Cirripedes. Almost all these names are applicable to the Balanida?, 

 or Sessile Cirripedes, and to the Verrucidse ■ but a few additional names are requisite, 

 which, together with the old names, will, I hope, be rendered clear by the accompanying 

 woodcuts. In Sessile Cirripedes, the whole of that which is externally visible, may, for 

 convenience sake, be divided into the operculum or opercular valves {valvce operculares)> 

 and the shell {testa), though these parts homologically present no real difference. The 

 operculum is seated generally some little way down within the orifice of the shell ; but in 

 very young specimens, and in Verruca, the operculum is attached to the summit of the 

 shell, and in these cases the shell, without the operculum be removed, can hardly be said 

 to have any orifice ; though, of course, the opercular valves themselves have an aperture 

 for the protrusion of the cirri. 



The shell consists of the basis (called the support by some authors), and of the com- 

 partments {testa valvce), which in recent specimens vary from eight to four in number, and 

 occasionally are all calcified together. 



The compartment, at that end of the shell (fig. 1) where the cirri are exserted through the 

 aperture or lips of the operculum, is called the carina (fig. 4) ; the compartment opposite to 

 it, is the rostrum (in all fossil specimens, like fig. 2), — these two lying at the ends of the 

 longitudinal axis of the shell. Those on the sides are the lateral compartmentsj that 

 nearest the carina, being the carino-lateral (fig. 3) {testa valva carino-lateralis), that 

 nearest the rostrum, the rostro-lateral, and middle one simply the lateral compartment 

 (fig. 3): but these three compartments are rarely present together. The rostro-lateral com- 

 partment, which always resembles fig. 2, and may be always known by having radii on 

 both sides, is. not known to occur in any fossil species ; and hence we are here only con- 

 cerned with the lateral and carino-lateral compartments. The compartments are separated 

 from each other by sutures, which are often so fine and close as to be distinguished with 

 difficulty. The edge of a compartment, which can only be seen when disarticulated from 

 its neighbour, I have called the sutural edge {acies suturalis). 



Each separate compartment consists of a wall {paries), or parietal portion {pp in figs. 1 

 and 4), which always grows downwards, and forms the basal margin ; and is furnished on 

 the two sides either with alee (fig. 4), or with radii (fig. 2), or with an ala on one side and 

 a radius (fig. 3) on the other. 



The radius (adopting the name used by Bruguiere, Lamarck, and others) differs 

 remarkably in appearance (though not in essence) from the wall or parietal portion, owing 

 to the direction of the lines of growth and the state of its usually depressed surface. In 

 the upper part, the radii overlie the alas of the adjoining compartments : in outline 



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