4 THE ENTOMOLOGIST. 



last are uninhabited. The isles are said to have been nearly 

 connected with the Land's End, durtng the Roman occupa- 

 tion of Britain ; and it is siijjposed that they were pre- 

 historically part of a large Atlantic continent, one of the 

 earth-waves which alternately rise and sink. There are 

 many proofs that the crags, now high above the sea, were 

 once within reach of the tide. Aphis Lychnidis occurs on 

 the Lychnis in St. Mary. The indiscriminate Aphis Rumicis, 

 often committing its offspring to plants that will not sustain 

 them, thrive here on the Mesembryanthemum. Tranaphis 

 Salicivora lives in St. Mary and iu Tresco on willow-leaves, 

 where it is accompanied by a little mite (Tetranychus 

 Salicis ?), and by an orange fungus; and the latter is the 

 food of a small red grub, perhaps of a Cecidomyia. Ixodes 

 Riciniis is common in Samson, and a species of Notaspis 

 occurs here and there in St. Mary. In addition to Epeira 

 diadema spiders occur of the genera Salticus, Thomisus, 

 Theridiou, Linyphia, Neriene, and Tetragnalha; they are 

 not generally numerous, but are extremely abundant on the 

 marshy ground near Forth Hollick, and indicate thatDiptera 

 are occasionally plentiful there. With one exception no 

 ground-spiders (Lycosa, Drassus, Clubiona, and Dysdera) 

 were seen, and in that respect these islands differ widely from 

 the Channel Isles, where the ground-spiders are very 

 plentiful in Guernsey. Lithobius forcipatus and a species of 

 Geophilus were of rare occurrence ; Oniscus asellus. Arma- 

 dillo vulgaris and Glomeris inargiuata were not very 

 abundant. The oak only occurs in the abbey grounds at 

 Tresco, where Dryobius roboris and Callipterus annulatus 

 have also been introduced. I did not see the Devonshire 

 galls there, but one individual of Cynips KoUari (lignicola) 

 was found, far from its native oak, in St. Mary, opposite 

 Tresco, and it was probably wafted from the latter isles by 

 the wind over three miles of intervening sea. Libellula 

 striolata is not uncommon in St. Mary, and Cloeon diptera 

 w as found in Tresco. Forficula auricularia and Stenobothrus 

 biguttulus are numerous in all the isles. The following list 

 includes, fifty-one species of frequent occurrence; those 

 that are less common will be mentioned afterwards. 

 Diptera. — Sciara morio, Dilophus spinatus, Scatopse notata, 

 Culex detritus ? Tipula oleracea, Ptychoptera contaminata, 



