SEA MUSSEL MYTILUS EDUUS. 217 



both rocky and sandy bottoms. The dog-whelk drills a hole from one and one-half times 

 to twice the diameter of that made by Urosalpinx and makes it in any part of the shell, 

 even through the umbo (fig. 202, opp. p. 216). The time required to make the perforation 

 varies from one to two days, according to the age of the mussel. On the rocky shore off 

 Sandwich, Mass., near the opening of the Cape Cod Canal, the author found the Purpuras 

 in great abundance on the scattered mussel beds, where the perforated shells of the latter 

 mollusk could be picked up by the handful. It was amazing to see the destructive work 

 that was being carried on by hundreds of these snails which could be seen adhering to 

 mussels here and there busily engaged at their deadly work. They preferred the young 

 shellfish which were about half an inch long. In one case two snails were found clinging 

 to the opposite sides of a young mussel. Further examination revealed that both animals 

 had perforated the shell at the same time and were competing for the maximum share 

 of the prize within. They eat the softer parts of the body first, leaving the edges of 

 the mantle and adductor muscles to the last. 



The snails, Lunatia heros and Neverita duplicata, sometimes called winkles, are 

 common all along our eastern coast as far south as Cape Hatteras and constitute an 

 important enemy of the mussel. The two species are much alike in habit and appear- 

 ance and may be easily confused. They are most readily distinguished by the thick, 

 dark lobe, which nearly covers the wide umbilicus, which is characteristic of the space 

 ventral to the opening of the shell of Neverita duplicata (fig. 198), but absent from that 

 of Lunatia heros (fig. 200). The latter species seems to frequent deeper waters than 

 does the former. They attack mussels and other mollusks with their rasping tongues, 

 which bear chitinlike teeth, and bore holes 3 to 6 mm. in diameter through the side of 

 the shell (fig. 199). The proboscis is then inserted through the opening and the con- 

 tents devoured. Quantities of mussel shells perforated by these predacious mollusks 

 have been dredged up by the steamer Fish Hawk in Vineyard Sound, which demon- 

 strate their destructive powers. 



The best measure of the devastation worked by Neverita duplicata on shellfish was 

 made by Mead and Barnes (1903). Their experiment was to invert an ordinary orange 

 box, which has two compartments, over a clam bed and sink it into the soil after 

 clearing away the surface debris. A single Neverita was placed in each compartment. 

 A fortnight later the contents of the box was examined. In one compartment neither 

 snail nor any perforated shells were found, while in the other the single Neverita was 

 found 5 inches below the surface of the ground with the perforated shells of eight 

 clams as witnesses of its voracity. This would indicate that the normal appetite of 

 these snails is satisfied with a clam or mussel once every two or three days. Snails 

 which the author kept in captivity with mussels during July and August refused to 

 eat at any time during that period. 



OTHER GASTROPODS. 



The conchs or winkles, Busycon carica (fig. 204, opp. p. 216) and B. canaliculala, 

 are supposed to be greater enemies of mussels, oysters, and clams than they really are. 

 Ingersoll (1887) states that these snails seize oysters with the concave under surface 

 of the foot and by muscular action crush the shell into fragments, then feed upon the 

 flesh thus exposed. He gave the estimate of one planter who believed that one winkle 

 was able to destroy a bushel of oysters in a single hour. Colton (1908), who carried 



