322 BALANID.E. 



fig. 1 b) : Lamarck attempted to express this appearance, by 

 using the specific name of stalactiferus. The colour of the 

 shell depends, to a considerable extent, on the colour of the 

 shelly matter in these exposed parietal tubes. We shall 

 presently see that the corrosion and disintegration, to which 

 some of the species are so liable, plays an important part 

 during their growth. The radii are either well developed, 

 as in most of the species ; or they are entirely absent, as in 

 the great majority of specimens of T. porosa and serrata. In 

 many individuals of T. porosa and purpurascens not only are 

 the radii absent, but the four compartments are calcified 

 together without any trace, on the external surface, of the 

 sutures. The largest specimen which I have seen of T. 

 porosa, which is the largest species, was two inches in basal 

 diameter, and nearly one inch and a half in height. 



Scuta. — These valves are sub-triangular, and either lon- 

 gitudinally or transversely elongated. Externally, the 

 growth-ridges are moderately prominent, and in T. costata 

 and ccerulescens they are crossed by longitudinal stria?. 

 Along the occludent margin, the inflected extremity of each 

 alternate growth-ridge is generally much thickened, — a set of 

 teeth being thus formed, by which the two valves are locked 

 together. In T. porosa, this character is variable, for some- 

 times every alternate ridge, and sometimes only two or 

 three ridges, separated from each other by several growth- 

 ridges, are thus developed into teeth. The articular ridge 

 is either moderately prominent, or is extremely prominent, 

 as in T. ccerulescens ; but the lower edge in no case depends 

 as a free, hinge-like style, as sometimes in Balanus. The 

 adductor ridge is generally well developed and distinct 

 from the articular ridge : in T.purpurasce7is it is very blunt: 

 in T. serrata it is united to the articular ridge half way up 

 it, thus forming a deep tubular cavity running up to the 

 apex of the valve : in T. ccerulescens, the adductor ridge is 

 very short, and is united to, or almost continuous with, the 

 lower end of the articular ridge, a small sub-cylindrical 

 tubular cavity being thus formed. Small crests exist for 

 the attachment of the rostral and lateral depressor muscles, 

 in most of the species, excepting T. purpmrascens and costata, 

 in which, however, more especially in the former, there are, 



