6 
in position, slightly in front of the pectoral, and imme- 
diately in front of the anus. As far as we have seen its 
fin rays never vary in number, and we have always found 
six on both sides. This is very striking when we consider 
the variability in the number of fin rays in all the other 
fins. 
The opercular fold or gill cover of the Plaice is large, 
and the branchial cavity opens behind by a wide aperture. 
This aperture is bounded on the inner side by the clavicle 
and on the outer side by the loose branchiostegal mem- 
brane supported by the branchiostegal rays. On lifting 
the opercular fold the gill-like pseudobranch is easily 
seen in a slight recess on the inner side of the operculum 
immediately over the dorsal extremities of the gill arches. 
Ventrally the opercular folds are separated by a conical 
fleshy mass containing the “ inter-clavicle,” and known as 
the isthmus. 
The lateral line of systematists commences on the 
tail, and courses straight forward at about the middle of 
the side of the body for the greater part of its length. It 
curves slightly upwards over the pectoral fin, and there- 
after becomes buried in the bones of the head. Further 
portions, however, of the lateral line system are visible on 
the surface, notably the right infraorbital canal under the 
right eye, and a portion of the supratemporal canal under 
the dorsal fin. 
The scales are mostly cycloid, but according to 
Cunningham (op. cz.) the so-called “ciliated” or 
“spinulated scale” is found only in mature males, and 
may form a conspicuous local peculiarity. The scales of 
this character that we have seen had three or four blunt 
processes on their posterior border. 
Regarding the apertures, the mouth is terminal and 
markedly asymmetrical. If the mouth of a plaice be 
