are _Pholas_ and a burrowing _Mytilus_, _under_ them are more _Conus_, _Dolium_, and huge frilled _Murices_. Patches of clean gravelly sand here produce _Strombus_; on the operculum of the great _Str. galea_ is sure to be a _Crepidula_, exactly fitting its breadth. On the liquid mud-flats to the north glide about _Marginella_, _Nassa_, and _Truncaria_, in the clean sandstretch to the west _Olivella_ ploughs about by hundreds with several species of _Natica_, and _Tellina_ and _Donax_ bury themselves deep, while farther down are _Artemis_, _Chione_, and, where mud begins to mix with the sand, _Mytilus_ and more _Arca_. Each of these species has its own habitat, often circumscribed to a few square feet at the most, and it would be utterly useless to seek for it anywhere except in its own special domain. Equally abundant are the land Mollusca of the tropics. Prof. C. B. Adams relates that within the limits of a single parish in Jamaica, named Manchester, which measures no more than four miles long and one mile broad, he obtained no fewer than one hundred species. Mr. J. S. Gibbons, in a description of the Mollusca he obtained near St. Ann’s, Curaçao, gives a lively picture of their abundance in an exceptionally favoured locality:--[2] “Near the outskirts of the town a waste piece of ground supplied me with occupation for all the time I had to spare. Neither grass nor water was to be seen, the only vegetation consisting of a few stunted cacti and still fewer acacia bushes. This, however, was so rich in shells that of several species enough specimens could have been collected in a few yards to supply, I should suppose, all the shell cabinets in the world.... The stones, plants, and ground were covered with _Strophia uva_ L., _Tudora megacheila_, P. and M., was in equal abundance, suspended by its silk-like thread from acacia boughs, or strewed thickly on the ground underneath. A _Bulimulus_ (_B. multilineatus_ var. _sisalensis_) abounded on the smaller boughs, while under masses of coral _Macroceramus inermis_ Gundl., _Pupa parraiana_ d’Orb, and _P. pellucida_ Pfr., were abundant. In the loose soil _Cylindrella Raveni_ Bland, _Cistula Raveni_ Bland, and a curious _Cionella_ were so numerous that a spade would have been the best instrument with which to collect them. I wasted a good deal of valuable time in separating them from the soil, when by simply taking away a few handfuls of mould, I might have obtained a larger number of specimens. A species of _Stenogyra_ and a _Succinea_ complete a list, all of which might have been gathered from almost any square yard of ground on the hillside.”