(sect, f), balanus imperator. 289 



specimen which I have seen was one and three-quarters of an inch in 

 basal diameter, the walls close to the basis being, in this instance, 

 actually *3 of an inch in thickness. 



Operculum thick and strong, covered by yellowish-brown epidermis ; 

 internally, the shelly substance is either all of the richest purple or 

 yellowish-white, tinged, especially in the upper part, with purple. 

 Scuta, with the apex beaked and somewhat reflexed ; articular ridge 

 very thick, little prominent ; articular furrow very narrow, the im- 

 pression made by the adductor muscle is seated very high up the 

 valve ; there is hardly an adductor ridge, but the surface of the valve 

 is angularly prominent in a curved line, running from the articular 

 ridge to near the rostral angle of the valve. At the rostral angle, the 

 occludent margin is not folded inwards, as is generally the case, but 

 the surface is flat, and is marked by four or five crests for the attach- 

 ment of the rostral depressor muscle. There are other crests for the 

 lateral depressor muscle. Tergum, with the apex somewhat produced 

 and beaked, but blunt; longitudinal furrow shallow ; spur of moderate 

 breadth, with its lower end rounded ; the basal margin on the carinal 

 side of the spur slopes towards it. Internally, articular ridge moderately 

 prominent. Crests for the tergal depressor well developed. 



Parietes, solid, thick, with the basal internal edge (4 c) formed of short 

 ridges, or flattened and irregular points, which in very old specimens 

 are but little prominent ; inner surface, finely, closely, and irregularly 

 ribbed longitudinally, but in some specimens nearly smooth. The 

 radii are nearly white ; they are narrow, sometimes hardly at all de- 

 veloped, and have their summits very oblique and jagged ; exteriorly, 

 they are sulcated in a transverse direction, and sometimes form oblique 

 steps, from having been formed layer over layer : their sntural edges 

 are formed of irregularly branching crests or septa. The alee have 

 their summits very oblique; their sutural edges are thick and crenated: 

 the part added during diametric growth on the inner surface is smooth, 

 and has a different appearance from the transversely ribbed portions of 

 the sheath, of which the alee form a portion. The lower edge of the 

 sheath is hollow beneath. The carino-lateral compartments are very 

 narrow. 



Basis calcareous, thin, white, sometimes opalescent, apparently 

 formed by an aggregation of very minute calcareous beads, with no trace 

 of furrows radiating from the centre. 



Mouth : labrum hairy, with apparently some very minute teeth ; 

 mandibles, with the fourth and fifth teeth small and rudimentary ; 

 maxilla? rather broad, with a narrow and rather deep notch under the 

 two great upper spines : outer maxillae with the lower lobe very large. 



Cirri : First pair, with the rami unequal by several segments : 

 second pair, with the rami unequal in length by about six segments : 

 third pair elongated, with the segments very numerous, almost equalling 

 those in the sixth cirrus ; upper segments of both rami much elongated, 

 each with only a circle of spines ; segments in the above first three 

 pairs of cirri only slightly protuberant. Posterior cirri elongated, with 

 the upper segments bearing three pairs, and the lower segments four 

 pairs of main spines, between which there is a small intermediate tuft. 



19 



