430 THK ZOOLOGIST. 



A considerable proportion of the food-supply at Eyebrouglity 

 is derived from the oil-shales in the bay west of Weak Law. 

 The collections made here in the course of the winters 1911 and 

 1912 show a steady seasonal fall in the sizes of Tapes and 

 Modiolus, and confirm the results for Mytilus in the same area. 



Table 4, Showing the Seasonal Diminution in Sizes of Opened Shells 

 of Modiolus and Tapes from "Shales," Eyebrouglity : Winter 

 1911-1912. 





Modiolus 









Tapes. 





Date. 



No. 



Average. 



No. 



Average. 



Nov. 



30th, 1911 



8 



5-0x2'5 cm. 



6 



3-0x2-3 cm. 



Dec. 



11th, 1911 







6 



2-6x2-2 cm. 



Dee. 



26th, 1911 



8 



2-8x1-55 cm. 





. . . 



Dec. 



27th, 1911 







32 



2'4xl"5 cm. 



Nov. 



18th, 1912 



13 



4-9x2*4 cm. 







Nov. 



28th, 1912 







20 



2-6x2-0 cm. 



Dec. 



12th, 1912 







15 



2-3x1-7 em. 



Dec. 



17th, 1912 



38 



2-3x1-3 cm. 







The Limpets are more abundant on the shales than are 

 Tapes and Modiolus. Though they are largely fed upon, the 

 Limpets show great recuperative powers. Grouped in the two 

 fortnightly periods for November, 1912, the results do not show 

 an appreciable change. When, however, separate returns are 

 taken from a fortnightly feeding period, a gradual fall appears 

 in the averages. 



Table 5, Shoiving Seasonal Average Sizes of Limpets fed upon by 

 Oystercatcher : " Shales," Eyebroughty, November, 1912. 



Date. 





Number. 



Average. 



November 15th, 



1912 



53 



2-2 x 1*5 cm. 



November 28th, 



1912 



66 



2*0 x 15 cm. 



November 12th, 



1912 



8 



2-7 x 2-0 cm. 



November 14th, 



1912 



24 



2-3 x 1-4 cm. 



November 18th, 



1912 



19 



1*9 x 1*5 cm. 



In the summer habitats each pair has an habitual range in a 

 nesting area and in a local feeding-ground. The boundaries, 

 where the range of one pair meets those of adjacent pairs, are 

 elastic ; depending, in part, on the presence or absence, at the 



