450 BALANID.E. 



ridge, of which only traces can rarely be detected in Balanus; 

 hence in these cases, as in C. Hembeli (PI. 18, fig. 5 a, 5 c) 

 and scabrosus (PI. 19, fig. 2 a, 2 c), the line of articulation 

 between the scutum and tergum is more complicated than 

 is usual. There is generally a slight pit, sometimes even 

 furnished with small crests, for the lateral scutal depressor 

 muscle : in C. scabrosus (fig. 2 d, q) a part of this muscle is 

 attached to a small pit at the basi-scutal corner of the tergnm, 

 — a fact of which I have observed no instance in any other 

 genus. In C. inter textus the terga and scuta are calcified 

 together, without even a suture being visible on their 

 internal faces. In C. Hembeli the valve is externally marked 

 by a few longitudinal furrows. 



The Terga, like the scuta, have a prominent articular 

 ridge and deep furrow. In many specimens of C. stellatus 

 and in C. scabrosus the valve is narrow : in C. Jlssus it is 

 triangular and nearly equilateral. The crests for the de- 

 pressores muscles are well developed : in C. scabrosus (PL 1 9, 

 fig. 2 d, p) these crests are united into a plate, which, together 

 with the outer lamina of the valve, forms a deep narrow pit : 

 in C. Hembeli the crests are furnished with small sub-crests. 

 The opercular membrane is narrow ; it is sometimes fur- 

 nished with a few minute spines. 



Structure of Parietes. — The parietes are solid, and 

 composed of successive layers of shell ; the inner surface 

 varies in condition in the same species, being either smooth 

 or marked with branching impressed lines, or mamillated, 

 or often irregularly punctured for the entrance of tubuli. 

 Owing to these tubuli, the walls, w r hen externally disinte- 

 grated, often become punctured. In certain depressed 

 varieties of both C. stellatus and scabrosus the walls are sup- 

 ported by irregular depending columns, placed along either 

 one side or both sides of the sutures. In C. intertextus we 

 have the remarkable character of the wall of the shell grow- 

 ing (I presume after a certain age) almost rectangularly in- 

 wards, thus forming a rather wide, flat, calcareous rim round 

 the central basal membrane. In C. Hembeli the internal basal 

 edges of the parietes, in one moderately young specimen, 

 were rugged with irregular points, but presented no other 

 remarkable appearance ; but in five old and very large spe- 



