In _Galathea strigosa_ the scales are convex, distant from each other, smooth at the edge, and fringed with long hairs. In _G. squamifera_ they are convex, closely placed, scalloped at the edge, and without hairs. In _G. nexa_ the scales are obsolete, tufts of hair representing the supposed edges. In _G. depressa_, n. sp., the scales are broad, less convex than in _G. strigosa_ and _G. squamifera_, smooth, closely set, and fringed with short hairs. In _G. Andrewsii_ they are small, distant, very convex, tipped with red, and slightly furnished with hair. As another instance of the practical application of the microscopical examination of the surface, I would refer to two species of Amphipoda, classed by Leach under the name of _Gammarus Locusta_, from his inability to assign them any separate specific characters. In the structure of their integuments, however, these two forms will be found to exhibit widely different microscopical appearances. Again, there exists in the same group three or four species, the description of any one of which would apply to either of the others; and it is probable they would never have been ranked as separate species had not their habitats been geographically distant. Thus _Gammarus Olivii_, M.-Ed., _G. affinis_, M.-E., _G. Kroeyii_, Rathke, and _G. gracilis_, R., can only be specifically determined by a microscopic examination of the integument. The same may be said of other Amphipoda, such as _Urothoe inostratus_, Dana, from South America, which so nearly resembles in form the _U. elegans_ of the British shores. GALATHEA DISPERSA, mihi. _G._ rostro brevi, dentibus 4 utrinque ornato, 2 anterioribus minoribus; pedibus anterioribus elongatis, sparse spiosus; chelarum digitis parallelis. Galathea with short rostrum, armed on each side with 4 teeth, the two posterior being less important than the two anterior. The fingers of the chelae impinge through their whole length; outer margin of the hand furnished with 3 or 4 small spines. _Hab._ Trawling-ground, Plymouth, common; Moray Frith, Scotland. This species unites _G. Andrewsii_ with _G. nexa_, and, I think, has often been mistaken for the young of the latter; but _G. nexa_, so far as my experience goes, is a species peculiar to the north of England, whereas _G. dispersa_, I anticipate, will be found to be the most universally dispersed, in deep water, of any of the species known. It can always be detected from _G. nexa_ by the form of the hand and the manner in which the fingers impinge: in _G. nexa_ the hand is broad towards the extremity, and the fingers meet only at the apex; in _G. dispersa_ the hand gradually narrows to the apex, and the fingers meet each other through their whole length, the inner margin of the finger being finely serrated, the thumb not. It also may be distinguished from _G. Andrewsii_ by the breadth of the hands, which are narrow and round in _G. Andrewsii_, and moderately broad and flat in _G. dispersa_.