OYSTER-BEDS OF LOUISIANA. 91 



DESTRUCTIVE AGENCIES. 



Conch, Snail, Borer. — The mollusk which is known by these names 

 on the coast of Louisiana is the Purpura floridana of naturalists. It 

 causes considerable damage at times to both the planted and the nat- 

 ural beds, especially those located nearer the sea where the prevailing 

 density of the water is higher, as it appears to be much more suscep- 

 tible to the effects of fresh water than the oyster itself. There is a 

 difference of opinion among the oystermen concerning the manner in 

 which this mollusk destroys the oyster, some contending that it bores 

 a hole in the shell like the northern drill, and others that it injects 

 between the lips of the shell a substance which possesses the power of 

 paralyzing the oyster and causing the shell to gape so as to permit 

 access to the interior. Some of the oystermen pointed out what they 

 considered to be the borings of this snail, but they were merely the 

 bottoms of the chambers made by Martesias, the upper portions having 

 disappeared by the delamination of the shells. 



During the eutire period of the investigations, although many bush- 

 els of oysters and dead shells were examined, not a single drilled oyster 

 shell was noted, although several Polinices shells showed the handiwork 

 of some boring gasteropod. 



A number of specimens of Purpura were kept in aquaria with oysters, 

 but in no instance did they molest them in any way. The theory that 

 they inject a poisonous fluid into the oyster can be set aside as improb- 

 able, and there can be little doubt that they destroy their prey after 

 the manner of their relatives, among which can be numbered the de- 

 structive drill, Urosalpinx, of Chesapeake Bay. This form, by means of 

 its rasp-like tongue, bores a small hole in the shell of the oyster, 

 through which it introduces its proboscis and extracts the soft parts. 

 Urosalpinx feeds upon small oysters only, but the conch of the Louisi- 

 ana oyster-bed, owing to its greater size and strength, could doubtless 

 attack much larger individuals with success. It is said that extensive 

 beds are sometimes practically depopulated by this animal, and the 

 oystermen of St. Bernard Parish hold it responsible for the destruction 

 of the oysters of Chandeleur Sound and for the present rather sparse 

 population of Cabbage Beef. It is found everywhere on the oyster- 

 beds of Louisiana excepting the less saline waters. It breeds in spring, 

 its eggs being inclosed in vase-shaped capsules, attached to hard bodies 

 in the water. Its numbers could doubtless be materially reduced were 

 the oystermen to carefully destroy all animals and their eggs which 

 they may take in the course of their work. Apparently little attention 

 is paid to this matter, and most of the snails caught are thrown back 

 on the beds with the culls and dead shells, to continue their destruction 

 and to perpetuate their kind. 



Drumjisli. — The drumfish is one of the most destructive enemies of 

 the oyster, and in Louisiana its depredations are especially annoying, 

 inasmuch as they are largely confined to planted beds of single oysters. 



