220 GENUS SCALPELLUM. 



narrowness of the branches of the corallines, to which it 

 has to adhere : a large circular disc, as in Lepas, would 

 have been worse than useless : the ultimate segment in 

 most or all the species, has on its inner side (the segment 

 being supposed to be extended straight forward) a notch 

 or step, bearing, I believe, two spines. 



Size and Colour. — Some of the species attain a medium 

 size, others are small. The valves are generally clouded 

 red or pink, but sometimes white. 



Mouth. — The various parts vary far more than in any 

 genus hitherto described. The labrum is highly bullate, 

 with the upper part forming a rounded overhanging 

 projection, and with the lower part much produced, so 

 that the mouth is placed far from the adductor scutorum 

 muscle, and consequently the orifice is directed more 

 towards the ventral surface of the thorax than in most 

 other Cirripedes : on the crest of the labrum there are 

 some very small teeth in several of the species, but not 

 in all. The mandibles have either three or four main 

 teeth, generally with either one or two small teeth inter- 

 mediate between the first and second large teeth, and 

 in the case of S. Peronii, with small teeth between all 

 the larger ones. The maxillae have their edges furnished 

 with many spines, and are either straight or have the 

 inferior part prominent and step-formed. The outer 

 maxillae have the spines on their inner edges either con- 

 tinuous or divided into two groups, of which latter struc- 

 ture we have not hitherto had any very well characterised 

 example. The olfactory orifices are either highly or 

 moderately protuberant. 



In most of the species the prosoma is little developed, 

 and the first cirrus is placed far from the second. The 

 Cirri are generally but little curled, and have elongated 

 segments, with long, generally serrated spines : the first 

 cirrus varies in proportional length ; the second and 

 third cirri have both their rami more thickly clothed with 

 spines than are the three posterior cirri, the spines being 

 generally arranged in three or four longitudinal rows : 



