_Relative position of parts._--The centre of the generally flat basis, which is cemented to the supporting surface, is properly the _anterior_ end, and the tips of the terga, often hidden within the shell, are properly the _posterior_ end of the external covering; but I have found it more convenient to speak of the _upper_ and _basal_ surfaces and aspects, which hardly admit of any mistake. A line drawn from the centre of the basis, along the middle of the rostrum to the tips of the scuta, shows the strictly _medio-ventral_ surface of the shell; and another line drawn from the centre of the basis, along the carina, to the tips of the terga, shows the strictly _medio-dorsal_ line; but from the crooked course of these lines, I have found it far more convenient to speak of the _rostral_ and _carinal_ end or aspect of the different parts of the shell; this is the more necessary with respect to the internal parts of the animal, owing to their remarkable changes of position during the metamorphosis, whence it comes that the dorsal surface of the thorax faces partly dorsally, partly anteriorly or downwards, and partly even ventrally; and the ventral surface of the whole posterior part of the thorax faces upwards or posteriorly; but when we refer these parts to the _rostral_, _carinal_, _basal_, and _upper_ ends of the shell, there can be no mistake. There has moreover been great confusion in these relative terms, as applied by different authors. When a sessile Cirripede is held in the position in which they have generally been figured, namely with the basis downwards and the scuta towards the beholder, then the _right_ and _left_ sides of the Cirripede correspond with those of the holder. I have followed the example of Botanists, and added the interjection (!) to synonyms, when I have seen an authentic specimen bearing the name in question. Every locality, under each species, is given from specimens ticketed in a manner and under circumstances appearing to me worthy of confidence,--the specific determination being in each case made by myself. CLASS--CRUSTACEA. Sub-Class--CIRRIPEDIA. _Crustacea attached by the anterior end of the head, by cement proceeding from a modified portion of the ovaria; archetype composed of seventeen segments, with the three first of large size, and almost always developed into a carapace, not wholly exuviated, and capable of various movements; antennæ none; eyes rudimentary; mouth prominent, formed by the partial confluence of the labrum, palpi, mandibles, and two pairs of maxillæ; thorax attached to the internal sternal surface of the carapace, generally bearing six pairs of captorial, biramous, multiarticulated limbs; abdomen generally rudimentary; branchiæ, when present, attached to the under sides of the carapace; generally bisexual, when unisexual, males epizoic on the female; penis single, generally probosciformed, seated at the posterior end of the abdomen; oviducts none; metamorphoses complex._