102 



in the posterior end of the body is much more openly fenestrated in 

 E. parma than in E. excentricus. 



I may add here an observation regarding the rate of growth of this 

 sea-urchin. On the place mentioned above, where the species was found 

 in such vast numbers, careful search was made also for the young speci- 

 mens, the sand being sifted through a sieve, the meshes of which were 

 only 1 D mm. No specimens smaller than 4 mm length were found. As it 

 was just in the breeding season of the species, it was, evidently, impos- 

 sible that the brood of that year could already have reached a size of 

 4 mm or even more, so that these young specimens must represent the 

 brood from the foregoing summer, being thus one year old. 



When measuring the whole material collected at this locality (in the 

 end of June and the beginning of July) the arrangement of the sizes 

 shown in the adjoining table resulted. It is quite evident therefrom that 

 the group from 4 17 mm represents the one year old specimens, the 

 main number of them measuring 5 10 mm. Another group from 20 

 52 mm, with the maximum from 30 40 must represent specimens two 

 years old, while the specimens from 55 70 must be, at least, three years 

 old. There is, however, no distinct limit between these two groups and the 

 possibility that the larger specimens are more than three years old cannot 

 be denied. - - As we do not otherwise possess any definite knowledge of the 

 rate of growth in Echinoids, the facts given here may claim some interest. 



Table of measurements of specimens of Echinarachnius excentricus from Gabriola 



island, June July 1915. 



mm Number of Number of Number of 



specimens specimens specimens 



3 26 1 49 



4 2 27 3 50 3 



5 16 28 3 51 



6 33 29 52 4 



7 54 30 4 53 



8 35 31 4 54 



9 34 32 1 55 2 



10 18 33 6 56 



11 10 34 4 57 5 



12 6 35 2 58 



13 ;, 36 2 59 2 



14 4 37 1 60 3 



15 2 38 5 61 3 



16 1 39 2 62 2 



17 1 40 6 63 1 



18 41 2 64 3 



19 42 65 4 



20 2 43 2 66 5 



21 44 4 67 6 



22 1 45 2 68 2 



23 46 3 69 



24 1 47 2 70 2 



25 48.. .2 71 



