16 G. O. Sars. 
ticles being interposed between somewhat larger ones. The 
caudal claws are rather slender, and without any setæ at the 
base, whereas their outer part is distinctly denticulated 
along the concave edge. 
The colour, in the living state of the animal, was a dark 
reddish brown, the concentrie ridges of the shell being 
considerably lighter. From the umbones, moreover, an 
| opaque whitish stripe was seen extending obliquely in front, 
and just behind it, between the 8th and 10th ridge an oval 
area was faintly traced, indicating the insertion of the 
adductor muscle of the shell. 
Biological Observations. 
Of this beautiful species some few specimens developed 
in my aquaria; but of these only a solitary individual 
attained full maturity. When first observed (on the 31st 
May), this individual had long since passed through the larval - 
period, the shell showing already 2 or 3 lines of growth. 
It rapidly increased in size during the next month, the shell 
gradually acquiring at the same time a greater number of 
lines of growth, until 14 such lines, all very strongly marked, 
were counted. After that time apparently no more such 
Jines were formed; but the marginal area was seen slowly 
to increase in size, so as at last considerably to exceed in 
width the interspaces between the lines of growth. On the 
30th June the individual was taken up and subjected to a 
closer examination under the microscope. It showed itself 
at once to be a fully grown female carrying a very dense 
cluster of eggs inside the shell. After a coloured drawing 
had been made from the specimen, while still alive, it was 
carefully preserved for subsequent examination. 
