I. 



Some Shell-borinor Alo^ae. 



A NOTE in the February number of Natural Science (i), to the 

 effect that botanists seemed incHned to keep to themselves in- 

 formation on the subject of shell-boring algae, suggested that it might 

 be of interest to readers if some account of the results of the investi- 

 gation of these plants by MM. Bornet et Flahault (2) were forth- 

 coming. The gradual disappearance of the empty shells of bivalves 

 and other molluscs has, until recently, been regarded as the result of 

 their disintegration by the friction produced by the movements of the 

 sea-water, and by the slowly dissolving action of the sea-water, charged 

 with carbonic acid. No doubt this explanation holds good in part, 

 especially for localities where the sea is " wild." In quiet, more or 

 less land-locked bays, another, and to the naturalist much more in- 

 teresting, cause is now known to contribute to the disappearance of 

 the empty molluscan shells. During the last fifty years many 

 naturalists have made known the presence of tubes of various kinds, 

 branching, and penetrating in different directions, into the substance of 

 fossil and recent corals, fish-scales, and molluscan shells. The late 

 Professor M. Duncan ( 3 ) gives, in " On some Thallophytes 

 parasitic within recent Madreporaria," a summary of earlier in- 

 vestigations of the subject, and adds considerably to it himself. 

 Unfortunately, the botanical aspect of the question is by all 

 ignored or misunderstood, the tubes are considered to be parasites 

 living on the organic matrix of the shell or coral, and are of interest 

 chiefly as illustrations of the persistence, through long ages, from the 

 Silurian to the present time, of identical or almost identical lowly 

 organisms. Thus the boring tubes are ascribed to '■'■ Saprolegnia or 

 Achlya, a confervan, a fungus with green coloring matter, if indeed, 

 Saprolegnia can be considered a fungus." Two species, Achlya 

 penetrans a.nd Achlya (Saprolegnia) ferax, Ktz., are recognised by Duncan, 

 but with this reservation : — " The classificatory position of the 

 parasite is in the midst of a group of forms which have complicated 

 life-cycles, such as the Achlyans (proper), the Saprolegniag, the 

 Empusinse and Botritidae, and the filamentous false-root bearing genera 

 Codiiim and Bvyopsis — forms which are more or less the expression of 

 one organism under different conditions and age." Professor 

 Duncan's investigations were mainly concerned with corals, of which 



c 



