The genus _Cortinarius_ is the largest genus of agarics in the British Isles, indeed in Europe and North America--perhaps in the world. It includes some of our most beautiful agarics, yet it is one of the least satisfying to the mycologist because of the difficulties experienced in identifying collections--partly because many species are so seldom seen. _Cortinarius_ contains just under two hundred and fifty recognisable British species, although recent research has shown that many more are yet to be described from this country as new to science. Except for some very characteristic species the individual members within the genus _Cortinarius_ are often very difficult to separate one from the other; however, _Cortinarius_ is one of our least difficult genera to recognise in the field owing to the presence when mature of rust-coloured gills and a cobwebby veil which extends from the margin of the cap to the stem. This structure is termed a cortina (Fig. 14) and in young specimens covers the gills with delicate filaments. As the cap expands the cottony or cobwebby filaments are stretched and either disappear entirely or may collapse to form a ring-like zone of filaments on the stem. In some species a second completely enveloping veil is also found, and this veil is viscid in one distinct group of which _C. pseudosalor_ already described is a member. The gills in the genus are variable in colour when young although constant for a single species; they may be lilaceous purple, orange, brown, red, yellow-ochraceous or tan, but ultimately in all members at maturity they become rust-colour. The spores under the microscope are richly coloured, yellow to red-brown and are frequently strongly warted; in mass they are rust-brown and this character coupled with the presence of the cobweb-like veil characterises the genus. Within the genus _Cortinarius_ there is a wide range of characters varying from species with distinctly sticky caps and stems, some with sticky caps and dry stems to those with both dry caps and stems. A few species are very large and fleshy whilst others are quite slender and many of the latter rapidly change colour on drying out and are then said to be hygrophanous. However, although there is such a large spectrum of characters in a single genus the species all have in common the cortina and rust-coloured gills, the latter often appearing as if powdered with rusty dust. Utilising the characters mentioned above this very large genus can be split into the following six sections, called by the mycologist subgenera: a. Large to medium sized fleshy agarics with viscid caps and stems--_Myxacium_ b. Large, fleshy agarics with viscid or tacky caps when fresh but dry stems--_Phlegmacium_ c. Large to medium sized agarics with dry, scaly or humid caps and dry stems which if orange tawny are robust--_Cortinarius_