A TROPICAL BEACH 



variety of station, abounds in niolluscan life to an extent which 

 must literally be seen to be believed. The beach at Panama, to 

 select an instance familiar to the present writer, is astonishingly 

 rich in species, which probably amount in all to several hundreds. 

 This is due to the immense variety of habitat. On the rocks 

 at high-water mark, and even above them, occur Trmicatella , 

 Mclampus, Littorina, and Siphonaria ; where a mangrove-swamp 

 replaces the rock, on the branches overhead are huge Littorina, 

 while three species of Cerithidea crawl on the mud, and Cyrena 

 and Area burrow into it. Lower down, in the rock pools at 

 half- tide mark are Cerithium, Purpura, Omphalius, Anachis 

 (2 sp.), JVassa, and several Crepidula. At low -water mark of 

 ordinary tides, under stones half buried in clean sand, are Coecum 

 and Vitrinella ; under the blocks which rest on solid rock are 

 Cypraea (4 or 5 sp.), Cantharus, more Anachis, Coluiiibella (3 

 sp. including the graceful C. harpiformis), and Nitidella. Where 

 the blocks of rock are rather muddy, Comis lurks, and with it 

 Turritella and Latirus. Where the rocks form a flat -topped 

 platform 2 or 3 feet high, with here and there a deep crack, 

 huge Chitons 3 inches long conceal themselves, with two species 

 of Turlo, Purpura and Clavella. At extreme low -water mark 

 of spring tides, on the isolated rocks are Monoceros, Leucozonia, 

 and Vermetus, in them are Pholas and a burrowing Mytilus, 

 tender them are more Conus, Dolium, and huge frilled Murices. 

 Patches of clean gravelly sand here produce Stromhus ; 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 MargineUa, JVassa and Trunearia, in the clean 

 sand -stretch 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 

 Area. Each of these species has its own habitat, often circum- 

 scribed 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. 



E(jually abundant are the land Mollusca of the tropics. Prof. 

 C. P. Adams relates that within the limits of a single parish 

 in Jamaica, named Manchester, which measures no more than 

 I'dUi- miles long and one mile l)road, he oljtained no fewer than 



