THE SESSILE BARNACLES. 



333 



To the description of this species may be added that the labrum 

 has a rather deep median concavity but no notch. The edge is 

 densely set with minute spines, and below the edge there are shorter 

 spines set in groups. There are no " teeth " (fig. 99). 



The palpus has a series of long spines on the face, as usual in 

 Balanus and some Ckthamali, running into a group on the distal end. 

 Upper margin densely covered with much shorter spines. 



The third cirrus has long rami like the fourth. The lower seg- 

 ments are densely bristly, like those of the second cirri, but the 



FIG. 99. HEXELASMA CALLISTODERMA. a, EDGE OF THE LABRUM. 6. SMALL FART OF THE 



EDGE MAGNIFIED TO SHOW THE SPINES. C, SPINES FROM THE CENTRAL PART OF THE 

 LABRt'M, SOME DISTANCE BELOW THE MARGIN. 



median and distal segments bear two pairs of long spines as in the 

 later cirri. Dense tufts of hair rise from the inner faces of the 

 median segments. 



None of the cirri have " teeth " or spinules. The penis is not much 

 more than half as long as the sixth cirri, and has no basi-dorsal 

 point. There is no trace whatever of terminal appendages. 



The basis is entirely membranous in young individuals, and the 

 compartments are longitudinally ribbed inside and at the basal edges. 

 In the adult stage the basal edges of the compartments grow in- 

 ward, as in some species of Chthamalus, forming a ledge, thick 

 outwardly, but thin at its inner edge, which is often somewhat 

 scalloped or lobed. The true basis is partially calcified, there being 

 an extremely thin calcareous film over large parts of it in old indi- 

 viduals, but, so far as I have seen, not complete. It is not easy to 

 observe, since parts of this calcareous film adhere to the peripheral 

 ledge and the body when the barnacle is removed from its support, 

 and parts of it remain upon the support. The calcification is there- 

 fore less complete than in Pachylasma. 



