66 Zoology 



(Mont.). On the other hand, the gravels contain several species that have 

 not yet been reported aUve in Cambridgeshire. Some of these, such as 

 Ena montana (Drap.) and Helicodonta ohvoluta (MiiU.), still hve in other 

 parts of England; others, such as Clausilia pumila (Pfr.) and Corbkula 

 Jiuminalis (MiiU.), are now found ahve only on the Continent; and one 

 or two, such as Helicella crayfordensis Jackson, seem to be wholly extinct. 

 In fact, the extensive river-gravel system of Cambridgeshire throws 

 valuable light on the gradual modification of its molluscan fauna from 

 middle Pleistocene times to the present day. It is possible, however, that 

 further search will show more living species than are at present known; for 

 although Cambridgeshire is rich in MoUusca, it numbers very few collectors 

 who are interested in these animals. 



ARACHNIDA' 



Records from the County comprise 245 spiders, 10 harvest spiders, and 

 7 pseudo-scorpions. The Acarina are not described. In collecting, the 

 Fenland has deservedly received the greatest attention and Wicken Fen in 

 particular. Neon valentuhs Falc. (a small dark Salticid), Maro suhlestus 

 Falc. and Centromerus incultus Falc. (small black Linyphiids), are unknowTi 

 elsewhere; Zora armillata Sim. has not been found elsewhere in Britain 

 (this is a pale speckly Clubionid) ; Maso gallica Sim. has also been recorded 

 only from Kent, Entelecera omissa Camb. doubtfully from Northumber- 

 land, and Shiga herii Hahn. doubtfully from Berkshire. 



May and June are the best months for collecting spiders at Wicken, and 

 on a sunny day careful search wiU reveal several of the so-called rarities 

 in abundance. Enclosed in silken cells in the fluffy heads of Phragmites 

 will be found the handsome Salticid, Marpessd pomatia Walck. Running 

 in the open, alongside the large velvety Pirata piscatoria Clerck and other 

 Lycosids, wiU be seen the lighter coloured Pardosa rtibrofasciata Ohl. 

 Amongst clumps of hay-coloured grass wiU be found both the pale 

 elongate Tibelli and another less common and also pale Thomisid, Thanatus 

 striatus C.L.K. Most of the rarities must be sought for by grubbing at the 

 roots of herbage or by turning over bundles of cut reeds: the black Zelotes 

 latetianus L.K., the small rather pinkish Cluhiona neglecta Camb., the large 

 tliick-set Lycosids Trochosa spinipalpis F. Camb. and T. leopardus Sund., 

 the speckly Salticid Sitticus caricis Westr. and such small uncommon 

 Theridiids and Linyphiids as Crustulina sticta Camb., Theridion blackwallH 

 Camb., T. instabile Camb., Taranuciius setosus Camb., Mengea warburtonii 

 Camb., Gongylidiellum murcidum Sim. and Wideria melanocephala Camb. 



' By W. S. Bristowe, Sc.D. 



