With respect to the variety from the West Indies, I have seen two sets of specimens differing somewhat in external appearance, one set attached to a coral from St. Vincent's, and another set to an Avicula from an unknown locality; at first I described these specimens, with some hesitation, as a distinct species, and I am very far from sure whether this would not have been the more correct course, although I am unable to point out any sufficient diagnostic characters. This form differs from the ordinary _B. spongicola_, in the walls being more rugged, stronger, and slightly or deeply folded longitudinally; in this latter case the shell in external aspect differs much from ordinary specimens of _B. spongicola_; but this is a variation so common that I dare not place any reliance on it. The colour is more purple; the summits of the radii perhaps rather less oblique. In the scuta the only difference is that the articular ridge seems rather longer, and the adductor ridge perhaps more prominent: in the terga, as already remarked, the basal margin on the carinal side does not slope so straight into the spur. These differences I consider all too slight to be of specific value. The difficulty in determining the nature of this variety is added to by its approach to _B. trigonus_ in all those points in which it departs from the ordinary _B. spongicola_, so that for a short time I was even tempted to consider both these species as varieties of one form. But until _B. trigonus_ is found with its scutum longitudinally striated, and with its tergum beaked, it can hardly be confounded with _B. spongicola_; for it should be observed that when in _B. trigonus_ the rows of little pits disappear from the scuta, as sometimes happens, though rarely, yet these valves do not become longitudinally striated. _Balanus spongicola_ occurs, mingled with _B. tulipiformis_, in the Mediterranean, and by the external characters of the shell alone cannot be distinguished from that species; but the striated scuta and beaked terga suffice to separate them. Again, this species, at the Cape of Good Hope, occurs mingled with _B. Capensis_, and from the non-striped young varieties of that species, it can, externally, be distinguished only by the beak of the tergum not being sharp like a needle. I have seen a single, perfectly characterised specimen, with its opercular valves preserved, found by Mr. S. Wood in the Coralline Crag at Sutton, mingled with _B. inclusus_. 16. BALANUS LÆVIS. Pl. 4, fig. 2-2 _g_. BALANUS LÆVIS. _Bruguière._ Encyclop. Meth. (1789), Pl. 164, fig. 1.[91] ---- DISCORS. _Ranzani._ Mem. di Storia Nat., 1820, Tab. 3, figs. 9 to 13. ---- COQUIMBENSIS. _G. B. Sowerby_, in Darwin's Geology of South America (1846), Tab. 11, fig. 7.