CONTRIBUTIOX TO AN EVALUATION OF THE SEA. 321 



district, and, further, since the size of the spat is what might be expected 

 from the following experiment and other observations, there can be little 

 doubt that they had settled on the raft and had grown in position, and 

 are therefore examples of the spat for that season. The spat obtained 

 varied in length from 4-5 mms. to 14 mms., and altogether 15 specimens 

 were obtained. Their average length was 81 mms. and their average 

 breadth 6-4 mms. Since they had grown during the time the raft was in 

 the sea, namely, from June 16th to October 2nd, their greatest possible 

 age is 15 weeks. 



At the same time as the experiment described above was begun another 

 experiment suggested by Mr. J. Bean, of West Mersea, was started for the 

 purpose of observing the rate of growth in the sea of young specimens 

 which were considered almost certainly a year old. For this experiment 

 Mr. Bean very kindly gave me the use of two of his oyster trays — which 

 are shallow wooden trays with one side covered with perforated zinc 

 and the other with small-meshed wire-netting — and also provided new 

 wooden posts, which are driven into the mud to carry the trays. The 

 travs were filled with shells and tiles secured to one side of the tray and 

 a number of young Crepidula were put on to the shells. A few older 

 specimens were marked and the shells on which they were sitting secured 

 to the tray. The total number of young specimens put in the tray was 

 131, and their average length 10-7 mms. They varied in size from 5 to 

 15 mms., but the commonest sizes were about 9 to 12 mms. These young 

 ones were put in the trays on June 18th and examined again on the 3rd 

 of the following October. When examined at the latter date a number 

 of them were found dead in the bottom of the tray and only 28 could be 

 found alive. These remaining specimens varied in length from 1-4 cms. 

 to 2-65 cms., and their average length was 2-1 cms., but 17 of them were 

 more than 2 cms. long. It is quite clear, however, that within the 

 period of the experiment, namely, 15 summer weeks, Crepidvdas about 

 1 cm. long grow to a length of two centimetres. Hence the spat obtained 

 in the former experiment may be regarded as a fair sample of the spat for 

 the season of 1913. Thus during the summer Crepidula spat grows to a 

 size of about a centimetre and appears to grow little during the winter, as 

 indeed was found by examining batches of the tiniest specimens pro- 

 curable on the grounds in the autumn and in the following late winter. 

 During the next summer the young slipper-limpets may grow to a length 

 of about an inch. This experiment is being continued and it is hoped to 

 follow the rate of growth further. Of the few larger marked Crepidula 

 put in this trav only two specimens showed an increase in size. One 



