398 



ECONOMIC AND TECHNICAL 



while Tegeocranus labyrinthicus, though usually a lichen-eating species, lives 

 either on mosses or on lichens on walls. Zopf 1 reckoned twenty-nine species 

 of lichens, mostly the larger foliose and fruticose kinds, that were eaten by 

 mites. Lesdain 2 in his observations on mite action notes that frequently the 

 thallus round the base of the perithecia of Verrucaria sp. was eaten clean 

 away, leaving the perithecia solitary and extremely difficult to determine. 



J. A. Wheldon 3 found the eggs of a species of mite, Tetranychus lapidus, 

 attached to the fruits of Verrucaria calciseda, Lecidea immersa and L. Metzleri, 

 calcicolous lichens of which the thallus not only burrows deep down into 

 the limestone, but the fruits form in shallow excavated pits (Fig. 126). The 



Fig. 126. i, Tetranychus lapidus, enlarged; i, Verrucaria calciseda with eggs in situ, slightly 

 enlarged ; 3 and 4, eggs attached to lichen fruits, much magnified (after Wheldon). 



eggs of this stone mite are found fairly frequently on exposed limestone 

 rocks, bare of vegetation, except for a few crustaceous lichens. "There is 

 usually a single egg, rarely two, in each pit apparently attached to the old 

 lichen apothecium. The eggs are very attractive objects under a lens ; they 

 measure -5 mm. in diameter, and are disc-like with a central circular depres- 

 sion from which numerous ridges radiate to the circumference, like the spokes 

 of a wheel. When fresh, they have a white pearly lustre, becoming chalk- 

 white when dry and old." Wheldon's observations were made in the Carnforth 

 and Silverdale district of West Lancashire. 



1 Zopf 1907. 



2 Lesdain 1910. 



' Wheldon 1914. 





