OF MASSACHUSETTS. 79 



But with the scallop we have the interesting case of an animal which 

 spawns but once and yet lives for nearly a second year, perishing just 

 on the verge of another spawning season, — an exact contradiction to 

 this principle. This apparent phenomenon might be explained in two 

 ways: (1) that a few second-year scallops are useful, as they spawn 

 twice; (2) that probably the shallow- water scallop (P. irradians) once 

 had a longer life and more than one spawning season, as its cousin the 

 giant scallop (Pecten tenuicostatus Mighels), and that the present Pec- 

 ten irradians is a decadent species. 



About the first of March the adult scallops begin to die, and this 

 period, when the average scallop is twenty months old, is taken as the 

 arbitrary beginning of the period of senescence. In the natural scallop 

 beds the majority of the scallops are caught by this time, while the re- 

 mainder sooner or later die a natural death, a large proportion perish- 

 ing before May or before the twenty-second month. This fact is well 

 known to seallopers who fish late in the season, and there have been 

 striking instances of large beds suddenly perishing, as at Dennis in 

 March and April, 1905. After May the length of life is variable, some 

 scallops passing the two-year limit (July) and occasionally living until 

 the following October and November (twenty-seven and twenty-eight 

 months), but the majority of these die before the twenty-fourth month 

 (July). Exact data upon this subject were obtained from scallops 

 which had been under observation in wire pens at Monomoy Point for 

 two years. Records of death-rate from old age show that, of 465 seal- 

 lops alive May 1 (twenty-two months), 32 per cent, remained by July 10 

 (twenty-four months) and only 6 per cent. August 2. In July these 

 scallops would have been two years old. Scallops one year old, con- 

 fined under similar conditions, showed only a slight mortality. 



It is, therefore, fair to assert that under natural conditions, when 

 unmolested by the seallopers, but 20 per cent, reach the two-year mark, 

 whereas on the scalloping grounds, unprotected both from nature and 

 man, the percentage of old scallops which reach two years is much less 

 than in the inclosed Powder Hole at Monomoy Point, and in all proba- 

 bility the total which pass the two-year limit is under 10 per cent. All 

 rules have their exceptions, and frequently instances occur where seal- 

 lops of twenty-eight months (recognizable from two growth lines and 

 general appearance) are found. In every scalloping ground an occa- 

 sional scallop of this age or older is dredged. More particularly, in 

 certain localities small beds of scallops which have passed the age limit, 

 are occasionally found, but usually the number in the bed is small. 

 Several small beds and one large (Common Flats, Chatham, 1908) have 

 come under the observation of the writer, who by no means claims 

 that the two-year limit is a hard and fast rule, but rather that there 

 are often exceptions, which, however, form but a small per cent, of the 

 whole. 



