Bryozoa, 'baniacles, calcai-eous tu'aes of Yerr-ilc-olaria and Aletes and other fouling organisms 

 (rig. 25) . Kezi^r of the shells v;ere so eroded and fragile that they easily cnunliled In 

 handling. Judging Tdv their condition, the shells were for several years ejrposed to the 

 action of sea v/ater after the death of the oyster. 



The largest number of dead shells (8O) was found at Station 18, at the northern 

 tip of Coi"ba Island. Locally the ground is kno'A^l as Coiha Channel. It was considered the 

 "oest pearling ground, which produced good shells and pearls. There were no small oysters 

 anong the dead shells found at this stationj all the specimens "brought "by the diver v;ere 

 fron 10 to 12 cm. long and had thick valves. 



In the ahsence of information on the rate of growth of the organisms v/hich foul 

 the shells on the Tjotton of the sea, it is impossihle to arrive at an^'- accurate estimate of 

 the time of death of these oysters. Judging lay tlie degree of erosion of shell substance, 

 I believe that they had been lying on bottom not less than five or six years. There was no 

 evidence that all the oysters died at the same time, for various stages of fouling and 

 decay of shell substance were found fron undamaged shells to those v/hich v;ere almost com- 

 pletely destroyed. (Tigs. 25 and 26). 



The starfish, which is such a destructive enemy of edible oysters in North 

 Atlantic waters, is very rarely seen on pearl-oyster grounds in Panama, and is not con- 

 sidled by local fishermen as an enemy of the pearl oyster. 



Pinctada nazatlanica , like Pinctada galtsoff i of the Hawaiian Islands, does not 

 grov; in large clusters, and neither species forms continuous beds or reefs typical of the 

 edible varieties of oysters. By its strong byssus, the pearl oyster is attached to rocks 

 and corals. Being scattered over a large area of sea bottom, the chances of attack by 

 drills and other predators are lessened in comparison with other sedentary mollusks which 

 live in close proximity to each other, or form extensive reefs. Divers whom I interrogated 

 on this subject informed me that they hever have been any mollusk or sea star feeding on 



figure 25 Dead shells of Pinctada mazatlanica . Eroded condition of shell substance 



and heavy grovrth of Bryozoa, Aletes (upper left on right shell) and other 

 forms, indicate that these shells remained in the sea for several years. 



l«D 



