:2:30 balainida:. 



septa, but in their upper parts are filled up solidly. The radii are 

 always very narrow, with their summits oblique, though to a variable 

 degree : their sutural edges have fine and closely approximate septa, 

 with minute denticuli : the sutural edges are received in a furrow, on 

 the opposed compartment, of unusual depth ; hence the lines of suture 

 run, in the lower part of the shell, almost exactly in the middle between 

 each two compartments. The aloe are added to above the level of the 

 opercular membrane. 



The Basis is often thick, with an underlying layer, largely cancel- 

 lated or honeycombed. When many specimens grow crowded together, 

 the basis is generally deeply cup-formed, or even sub-cylindrical ; and 

 equals as much as four fifths of the length of the entire shell. In such 

 cases, in some few recent specimens, and in all the large or even 

 quarter-grown old tertiary specimens, but not in the quite young fossil 

 specimens, a structure is presented, which I have not seen in any other 

 Cirripcdc, namely, the basis (PI. 4, fig." 2 a) is filled up for one 

 third, or even for more than half its depth, by successive, separate, 

 calcareous, transverse layers or septa. It would appear as if the basal 

 cup had grown too large for the animal's body, and so required filling 

 up. The layers are thin and fragile ; a single layer never stretches 

 across the whole shell ; each is irregularly mammillated or blistered, 

 with the convex surfaces generally directed upwards ; the layers are 

 furnished on their under sides with little pillars and short ridges, 

 resting on the layers beneath ; it rarely happens that the supports of 

 one layer lie directly over those of another, though this is sometimes 

 the case. In a vertical section, the mass formed by these irregular 

 layers has a coarsely cancellated structure. This structure, although 

 confined to this one Cirripede, is not so anomalous as might at first be 

 thought, for in most species of the genus, each time that the circum- 

 ference of the basis is added to, an excessively thin calcified film is 

 thrown down over its whole inner surface ; and in any of these species, 

 if the films had been formed thicker and had rested only on certain 

 points, instead of over the whole underlying layer, the cancellated 

 structure above described would have been produced. 



Mouth : the labium is either destitute of teeth, or has two or three 

 very minute teeth. The palpi have a tuft of very long spines at their 

 ends. The third tooth of the mandibles is thicker and larger than the 

 two upper ones. The maxillse have either a nearly straight edge, or 

 the inferior corner is obliquely truncated, and projects much beyond 

 the rest of the edge. In the Cirri, none of the segments are very pro- 

 tuberant : in the first pair, one ramus is nearly twice as long as the 

 other : in the posterior pairs, the segments are not much elongated, 

 but each supports seven pairs of spines. 



Var. nitidus : with respect to this variety I have little to add to my 

 preliminary remarks on its peculiar appearance, owing to its smooth, 

 naked condition, and pure white or pale purple colour. This colour, 

 when examined through a lens, is seen to consist of very fine longi- 

 tudinal stripes ; and is produced by the calcareous matter within the 

 longitudinal parietal pores being thus coloured. Generally the scuta 

 have two longitudinal furrows ; but I have seen a scutum of one per- 

 fectly characterised specimen with only a single broad furrow, like that 



