244 Mr. J. S. Gladstone on the [Ibis, 



ramus, giving a smooth, glazed appearance to the under 

 surface of the feather which is conspicuous at the most 

 casual glance/' 



My examination of the ventral ridge indicates that when 

 present in complete form it extends al)out lialf the length of 

 the barbs. It is widest at the rhachis end and tapers to a 

 fine point. Prior to perusal of Chandler^s Avork I named 

 this cover of the space between the barbs as the " tegmen,'^ 

 which for convenience I continue to use, as there is a 

 considerable difference between a ventral ridge and a fully- 

 developed tegmen. 



The tegmen is particularly developed in water- and game- 

 birds as well as in the Turkey. The Heron has a dark brown 

 ventral ridge which, though not large enough to form a com- 

 plete tegmen, is sufficient to create the general appearance 

 of tegmeuous structun^ but instead of a glazed surface it 

 resembles brown velvet when the feather is held at a suitable 

 angle to the light. I find this Heron-like structure is not 

 uncommon, but as it does not come under the head of 

 "a, tegmen'^ the subject has not been specially studied. 



I find three types of barbs : — 



1. The flat barb, which may or may not have a ventral 



ridge and gives no indication wliateverof a tegmen. 



2. The curved barb, which, having a coloured ventral 



ridge, gives a tegmenous appearance to the under- 

 side of a feather. 



3. The flat or curved barb with fully-developed tegmen. 



Type 1 includes the Passeres, Picariee, Columbse, Fuli- 

 cariae, Alectorides, and Pygopodes. 



Type 2 is represented by the Accipitres, Steganopodes, 

 Herodioues, Pteroclites, and Limicolse. 



Type 3 is found in the Striges, Anseres, Gallinse, and 

 Gaviae. 



The following is a description of the photographs which 

 I have prepared in studying this structure : — 



Plate V. fig. 1 is a portion of the underside of a Pink- 

 footed Goose primary, magnified six times. The lower 



