SEA-FISHERIES LABORATORY. 33D 
first of these has been removed to the Filibranchia and 
the second to the Mulamellibranchia. 
We see, therefore, that the position of our type is 
as follows :— 
Class: Lamellibranchia. Ord.: Filibranchia. Sub- 
order: Pectinacea. Fam.: Pectinidae. Genus: Pecten. 
The American scallop, however, Pecten tenuicostatus, 
has, according to Drew (1), the gill filaments united by 
interfilamental vascular junctions, thus forming one 
exception to the definition of the Filibranchia, and 
serving to show how insufficient single characters may be 
in a scheme of classification. 
The genus Pecten is of world-wide distribution, 
though most of the species are confined to smaller areas, 
and the habitat extends from the littoral zone down to the 
450 fathom line and probably further. 
The distribution in time extends from the Cretaceous, 
and possibly it goes even further back to the Carbon- 
iferous period. Jackson ($) in his work on the Phylogeny 
of the Pelecypoda, has shown how this genus is related 
by the structure of the early nepionic shell to the 
Aviculidae, and in all probability the fossil Aviculopecten 
of the Devonian rocks was a connecting link, so that the 
ancestry of the Pectens can thus be traced back to Silurian 
times. 
In addition to Pecten maximus and P. opercularis— 
generally distributed in Huropean seas—the following 
species are found round the British coast :—Pecten pusio 
(Linné), Pecten varwws (Linné), var. purpurea, Jeffreys, 
and var. navea, Macgillivray, P. sulcatus (Miller), P. 
fragilis (Jeffreys), P. clavatus, var. septemradiatus, Miller, 
var. alba, Jeffreys, and var. dumasi, Payraudeau, P. 
tegerinus (Miller), and var. costata, Jeffreys, P. incom- 
parabuis (Risso), P. striatus (Miller), P. semalzs (Laskey), 
