STRUCTURE 01 MOUTH. 75 



cles, &c. removed, of Coronula. The mouth differs ex- 

 tremely little in the different genera and species of the 

 Balanidae, much less than amongst the Lepadidae. In the 

 Balaninse, the crest of the labium is sometimes hairy, in- 

 stead of having, as is usual, from two to six teeth on each 

 side of the central notch s in Balanus improvisus (PL 26, 

 fig. 2) and eburncus, and in Chelonobia, the crest on each 

 side of the central notch (e) is furnished with a row of finely 

 graduated teeth. A sub-triangular portion of the inner 

 fold of membrane of the labrum, which overhangs the 

 oesophagus, is always thickened and yellowish ; it is also 

 often punctured in patterns (PI. 26, fig. 2,/), which, I 

 believe, give attachment to little muscles that serve to open 

 the upper end of the oesophagus. Opposite to this thickened, 

 sub-triangular portion of membrane, the thin membrane 

 forming the supra-cesophageal cavity (or the cavity sur- 

 rounded by the gnathites) is strengthened by a pair of 

 curved ribs (h, fig. 2) of thickened yellowish membrane, 

 running down from the inner bases [a") of the bilobed 

 outer maxillae to the opening of the oesophagus (g) : a 

 broad branch from each of these ribs supports the sides of 

 the orifice of the oesophagus ; and this branch almost joins 

 on to a slightly thickened rim or bar (/'), which branches 

 off' from the upper part of the sub-triangular (/) inner fold 

 of the labrum. This structure, in Bal. improvisus, is repre- 

 sented in PL 26, fig. 2, as well as it could be, considering 

 that the deep supra-cesophageal cavity has to be torn open, 

 and then laid flat. 



The Palpi (PL 26, fig. 6) differ little, except in size, in 

 the different genera, being squarish, more or less elongated, 

 or even approaching to club-shaped : in most of the Bala- 

 ninae they are larger even than the mandibles, of which 

 they normally form a part. Their upper margins, especially 

 towards their free extremities, are always thickly clothed with 

 spines ; and there is generally a single row, either short (r) 

 or long, of spines of greater length, which arise from a little 

 above, and stand almost in a parallel line to, the basal 

 margin. On the internal surface, there is sometimes a 

 row {t) of very short little spines, which overhang the crest 

 of the labrum. The Mandibles (PL 26, fig. 5) have from 



