66 OYSTER BOTTOMS IN MATAGORDA BAY. 



closure of Mitchells Cut. The oyster grower must take this fact 

 into consideration, for beds overrun with mussels are not only less 

 productive, but the stock is liable to be inferior in condition and 

 external appearance and more labor is required to cull it. 



Borer, boring clam (Martesia cuneiformis). — During the survey 

 frequent reference was heard to the presence of borers upon certain 

 of the beds, but investigation developed that it was neither the drill 

 {Urosalpinx) of the Chesapeake nor the like-named snail {Purpura) 

 of the gulf coast which was so designated, but a comparatively harm- 

 less little clam. Neither upon the reefs nor among the specimens 

 exhibited by the oystermen was there found a single shell exhibiting 

 the work of a predatory snail. A few live specimens of Urosalpinx 

 were found, and on Half Moon Reef there were many egg cases of 

 Purpura, but it is evident that these organisms are not destructive in 

 these waters. 



The boring clam appears to be confined almost exclusively to Half 

 Moon and Mad Island reefs, being most abundant on the former, 

 where a large proportion of the shells are occupied by it. It in no 

 way preys upon the oyster, but merely utilizes the shell as a place of 

 abode and does but comparatively little harm. If either living or 

 dead oyster shells from Half Moon Reef are carefully examined, a 

 very large proportion of them will be found to exhibit numerous 

 small round holes, each fringed with a very short parchmentlike 

 tube. If the shell be carefully broken, each of these orifices will be 

 found to communicate with an egg-shaped cavity, narrow toward 

 the opening and broader toward the inner face of the shell, in which 

 is snugly lodged a little clam of corresponding shape. Often the 

 chambers are so numerous as to be almost in contact and the shell is 

 reduced to the structure of a honeycomb. In such cases it becomes 

 much weakened, the outer layer scales off, the clam drops out, and the 

 new surface exposed presents the bottoms of the chambers as a 

 mosaic of smooth hemispherical pits having the appearance of 

 drilled cavities almost penetrating to the inner face. It is this 

 appearance that generally attracts the attention of the oystermen^ 

 who apparently do not connect it with the small inconspicuous ori- 

 fices primarily existing. 



The boring clam first enters the shell when quite small and in- 

 creases the dimensions of its chamber as it grows, eventually attain- 

 ing a length of three-eighths of an inch. The boring of the chamber 

 sometimes perforates the shell, in which case the oyster throws down 

 new deposits of shelly matter to close the opening and produces 

 either a general thickening when the perforations are numerous and 

 close together *>r a series of slightly elevated lumps when they are 

 more isolated. The clam never attacks the oyster, but gets its food 



