water. Typically deep cupped, the cavity of the attached valve 

 extends under and beyond the hinge; this left valve is larger than 

 the free moving one. Inner margins of the valves are smooth and 

 undentioulated and usually are purple in color. The posterior 

 adductor muscle scar is non-pigmented and is distally located. 

 There is a promyal chamber. The sexes are separate and the eggs 

 and sperm are released in the water for fertilisation. 



One specimen of the larviparous oyster, Ostrea cristata Bom, 

 was oollected in Hurricane Hole on St. John, Virgin Islands. 



Some individuals were found with ripe gonads and there were 

 oyster larvae in the plankton samples oollected with the fine net. 

 Mattox (1948) reports that individuals were found throughout the 

 year with ripe gonads and that spawning takes place at all months 

 of the year* A similar situation has been observed in the oysters of 

 the Gulf of Mexico coast of the United States when, in an extremely 

 mild winter, oyster larvae are present and setting takes place on 

 cultch in abundant amounts through the year. There are slight peaks 

 of spawning, but these are less marked than in years of colder winters* 

 In warm years there is no period in which sexually mature and spawning 

 oysters ceuinot be found. It would be interesting to know if there are 

 any peaks in the spawning activity of the oysters of Puerto Rico and 

 the Virgin Islands, Mattox did not report any for Puerto Rioo, but 

 his completed observations have not been published. 



There was no evidence of shell damage frcrai the marine worm, 

 Polydora . This, of course, may be correlated with the method of 

 oyster growth on the vertical roots of the mangrove and off the bottcxa. 

 Examination of the mantle margin for the presence of the encysted spores 

 of the gregarine, Nematopsis , showed that this parasite was absent in 

 the oysters collected. 



Conditions affecting oyster production 



Conditions favorable for the production of oysters in any great 

 quantities are not present in the waters of the Virgin Islands and 

 Puerto Rioo. "Bie rugged coastlines with rooky shores where there is 

 considerable rough water and the few bays where the shore is either 

 rocky or has sandy beaches are not oyster-growing areas. Estuarine 

 waters, which are the most advantageous for oysters, are definitely 

 lacking. Tlie quiet lagoons offer the only areas where oysters grow to 

 any extent and where culture is at all feasible. Here the bottoms are 



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