Professor MacGillivray on the Cirripedia. 175 



feet have each a similar, gradually shorter filament from the basal joint ; 

 but the last pair has none. 



The narrowed part of the bodj', to which the five pairs of abdominal 

 feet are attached, is smooth and horny above, transversely grooved or 

 subarticulate beneath. It ends in a very long, slender, tapering tube, 

 usuall}' curved inwards, but when extended much, exceeding the last 

 cirri in length. At the base of this tube, on the dorsal aspect, is the anus, 

 over which are two oblong, mobile horny plates. 



The general colour of the body is white or pale yellowish-grey an- 

 teriorly, darker behind, the legs and cirri dusky-brown. 



There is a transverse muscle, as usual, and the fore-part of the body, 

 which projects far beyond the mouth, is rounded, but tapers into the 

 peduncular tube. 



The mantle is ver_v thin, generally pale yellowish-brown, minutely 

 variegated with darker brown, by the pigment. 



The tegmen ovato-globose, or subcylindrical, and somewhat com- 

 pressed, abruptly inflexed beneath, coriaceous, translucent, brown, 

 darker above, the margin of its aperture thick and reflexed ; the appen- 

 dages subovate, bursiform, puckered, and having a Itirge terminal aper- 

 ture, the dermal lining a continuation of the mantle, and generally per- 

 forated at the end ; five very small calcareous pieces. 



The anterior pair placed obliquely near the lower part of the opening 

 in the ventral margin, oblong, bent in the middle, laterally twisted, thick, 

 with the upper part broad, and abruptly rounded, the lower tapering, 

 narrow, and rather acute below, marked with concentric rugae, and ra- 

 diating striulaj ; the upper linear somewhat curved, nearly parallel, and 

 ending in two membranous points projecting over the aperture ; the 

 dorsal piece extremely small, often scarcely perceptible without a glass, 

 sometimes wanting. 



The peduncle generally longer than the tegmen, cylindrical, with a 

 circular groove where it joins the tegmen, smooth, glossy, or glistening, 

 coriaceous, brown, usually tinged with blue, paler toward the base, 

 where it is thicker. 



Some remarkable variations are exhibited by this species; — 

 Young individuals are not so membranous as those of Cincras mem- 

 branacea, but from the first have more or less of the coriaceous firmness 

 of the adult. I find that some of them have no appendages, others two 

 Tery small prominences, others roundish, subhemispherical, or ovate 

 bodies, always imperforate. In larger individuals, even up to two inches 

 in length, the appendages are often still imperforate, generally ovate, 

 seldom smooth, but mostly puckered in various degrees. As the animal 

 enlarges, they become proportionally longer and more bullate. Some- 

 times the epidermis at the tip is seen with an irregular slit, sometimes 

 with an interruption having a shred across it, sometimes with a round- 

 ish, but usually irregular discontinuity. Still, the inner or dermal mem- 

 brane may be entire ; but at length it opens at the end. In old indi- 

 viduals, there is a wide irregular opening in both membranes, and often 

 the appendages are torn into shreds at the end. In one large individual, 

 one of the ears has a large aperture, while the other has none. Under 

 these circumstances, one may judge what importance can be attributed 

 to characters taken from the aurifoiin sacs, as has been tried by some. 

 I apprehend that those from the precise form of the calcareous plates 

 arc equally' insufiicient. 



For example, the anterior plates are very narrow, thin, and little bent 

 in very young individuals ; broad above, thick, geniculate, and much 

 twisted in large specimens, obtuse or acute below. The upper valves 

 vary in like maaner from linear to subtriangular. The dorsal piece ia 



