A TROPICAL BEACH 



variety of station, abounds in molluscan 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 Truncatella^ 

 Melampus^ 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.), Oantharus^ more A^iacJiis, Columhella (3 

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

 the blocks of rock are rather muddy, Oonus 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 Turbo, 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, 

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

 Patches of clean gravelly sand here produce Strombus ; on the 

 operculum of the great Sir. galea is sure to be a Crepidula, 

 exactly fitting its breadth. On the liquid mud-flats to the north 

 glide about Marginella, JVassa, and Truncaria, in the clean sand- 

 stretch to the west Olivella ploughs about by hundreds with 

 several species of Natica, and Tellhia and Donax bury them- 

 selves deep, while farther down are Ai^temis, Chione, and, where 

 mud begins to mix with the sand, Mytilus and more Area. 

 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 



