Mollusca of the Laminarian Zone at Leith. 345 
Leith sands. The last gasteropod in the list is Z'wrritella 
terebra, Which is, of course, common. 
The Lamellibranchiata are abundantly represented, all the 
forms that occur on the east of Scotland on sandy bottoms at 
a depth down to that of a few fathoms being more or less 
well represented. In the following list the species are stated 
in the order of the numerical abundance of the individuals ; 
those which occur also in deposits of late glacial age being 
denoted by a prefixed asterisk :— 
*Tellina balthica, *Cardiwm edule; *Mya arenaria, of 
which a great number of shells, about one-third the size of 
the adult, occur in the position of growth; *Mya truncata, 
*Artemis lincta, *Tellina tenuis, *Tapes decussatus, Tapes 
pullastra, Solen ensis and Solen siliqua, * Venus striatula (or 
gallina), *Mactra solida, Mactra stuliorum, Mactra subtruncata, 
Venus fasciata, *Pecten opercularis, *Pecten pusio,; *Mytilus 
edulis, mostly drifted; *Nuwcula nucleus, *Corbula gibba, 
*Astarte compressa, *Leda minuta, *Cardium echinatum, 
*Cyprina islandica, *Lutraria elliptica, Syndosmya alba, 
Thracia phaseolina, *Donax vittatus, *Psammobia ferroensis, 
Cryptodon flexwosus. 
Saxicava, Pholas, Ostrea, were hardly to be expected on a 
bottom of loose sand. Anomia ephippiwm, of which two small 
examples were met with, probably came with seaweed. 
A glance at the list shows that, along with many shells 
that occur in the glacial deposits of Elie and Errol, there 
occur others that are not found in those places. Some few 
species common in deposits of late glacial age, and which 
have probably at one time lived here, are conspicuous by 
their absence. This is, of course, partly due to the conditions 
of bottom and depth under which the Mollusca found in the 
shelly sands at Leith have lived. But much of the difference 
arises from the numerous oscillations of level that have from 
time to time affected this part. This is almost as potent a 
factor in its relation to the well-being of the Mollusca that 
live in waters of no great depth as the amelioration of the 
climate. The other chief factor in bringing about the bio- 
logical change referred to has been the gradual immigration 
