Norwich Castle Museum. 125 
valves sometimes to a considerable thickness. Some 
specimens of detached pearls are also exhibited. 
Nearly related to the Oysters are the Pectens or 
Scollops, Mr. Jeffreys enumerates nine species, most 
of them, with many varieties, are in the collection. 
Some are very elegant and delicately coloured. 
Pecten maximus, the largest of the genus, is found 
on the Norfolk coast. When the Scallop is young 
it swims very freely and is extremely active. The 
second genus of this family, namely Zza, resembles 
the Pectens in some respects, but the shell is 
always white. Some of them dwell in an artificial 
burrow ; others spin a byssus. Mr. Jeffreys enumer- 
ates five species. Examples will be found in the 
collection. The next genus, Azula, contains 
oniy one species, known as A. firundo, from the 
fancied resemblance of its curiously-shaped shell to 
a swallow on the wing. It attaches itself by a byssus 
to objects at the bottom of the sea, and in the 
British seas has only been found off Plymouth. The 
inner surface of the shells is lined with pearly sub- 
stance, and is beautifully iridescent, like its near 
relatives the ‘‘ Pearl” and “ Hammer” Oysters. Of 
the giant Pinna and its beautiful silken byssus, we 
have spoken before (p. £.6) and now pass to the 
MytTitipaé, the type of which is MWytlus edulis, our 
well-known Mussel, which abounds in some localities 
on the Norfolk coast, and constitutes a valuable 
fishery, both for human consumption and as bait. 
There are several species and varieties, one of these, 
i. barbatus, is noticeable tor the shaggy beard with 
which its shell is adorned. Of the family Arcapa, or 
Arks, we have several representatives in each genus. 
Case I. 
Gegin with the important family Carprap., consist- 
