SEA-FISHERIES LABORATORY. 139 



of sand, with consequent absence of food ; and (2) Force of sea 

 and shifting character of sand. The number of castings per 

 square yard at Musselburgh and Portobello are given at from 

 12-15 to 34-38, and at Barrow, 10-24 (average 20). Davidson* 

 (quoted by Ashworth) estimated their numbers at Holy Island 

 at 82,423 per acre, and the sand brought up yearly at 1,911 tons 

 per acre, equalling a layer 13 inches deep. Thus in 22 months 

 the whole sand, two feet deep, would pass through their alimen- 

 tary canals. Their ova masses, anchored in the sand, are a 

 feature of many cockle beds during the spring months. 



Other worms found on the Ynyslas beds include Nereis 

 diver sicolor , Scoloplos armiger and Pygospio elegansf. 



Of Crustacea, CoropJiium vohitator (grossipes) abounds on 

 muddy areas near shore, and is seldom common on the cockle 

 beds, where the sand is generally too fine for the formation of 

 its burrows. Neomysis vulgaris and Crangon vulgaris% abound 

 on the Dyfi beds, etc., in runlets of water. Eurydice pidchra 

 is frequently met with swimming actively in shallow pools. 

 Small specimens of Carcinus mamas are frequently met with, 

 buried in the sand, all over the tidal region. 



Mollusca — Paludestrina stagnalis is a most abundant 

 form on those portions of the cockle beds nearest shore, and 

 of a somewhat firm and muddy character ; it is scarce or absent 

 on loose sands. Its egg masses were observed on May 26th, 

 1919, on the Traeth Lavan, exactly as described by Professor 

 Herdman for Hilbre Island in June, 1888, § and Lindstrom for 

 Gotland (quoted by Herdman) ; these ova masses are placed 

 upon the shells of the snails. I found 28 such masses upon a 

 sample of 18 specimens collected at random — 



*Geol. Mag., 1891. Dec. 



t I am indebted to Dr. E. J. Allen, F.R.S. for the identification of these. 

 + These species were kindly named by Dr. Caiman, of the British Museum. 

 § Fauna of Liverpool Bay, II. p. 8. 



