1904 — 5 .] Report on Medusae found in Firth of Clyde. 747 
sudden drop to 48° F., which was probably due to a long spell of 
cold easterly winds. During December the temperature was about 
48° F. until the middle of the month, and it decreased to 45*3° F. 
by the 30th. 
After allowing for short spells of extreme cold and hot weather, 
the records tend to show that the winter temperature was about 
44° F. and the summer about 54° F. 
There is an account of the physical conditions of the Clyde Sea- 
area by Dr EL R. Mill in the “Fauna of the Clyde,” and it 
contains tables showing salinity and sea temperatures in different 
parts of the Clyde. A table for 1887 shows that in the Arran 
basin (just south of the Cumbraes) the surface of the sea was 
coldest in February and March (42'9° F.), and warmest in August 
and September (55*2° F.). 
The Tow- nets. 
The tow-nets which were generally used during 1902 were 
similar in pattern and size to those used by me at Valencia. 
These nets have a circular mouth of 17 inches in diameter and 
are about 5 feet in length, gradually tapering down to 3J inches 
in diameter, which is the diameter of the zinc can attached to the 
end of the net. The nets were made of the usual Bolting silk, 
and the series consisted of four nets, having respectively 30, 50, 
60, and 76 threads per inch. The net used for each haul is 
recorded in the “Notes on the Pelagic Fauna,” p. 781. It must 
be remembered that a net, after it has been used for some time, 
becomes much finer; as the threads flatten and fray out, the 
meshes become smaller. As a rule, we used a net which ought to 
catch any organism about 0‘5 mm. in diameter. 
For general use I recommend a net with about 60 threads to 
the inch. This net (of the size mentioned above) wrnrks best with 
a pull of about 3 lbs., measured on a spring-balance; or, when 
sitting in the stern of a rowing boat, the pull on the net should 
not exceed the holding strength of one finger. 
