INTRODUCTION. 



Vll 



abundance in the first or Sheppey zone of Mr. Prestwich. This is the case even 

 with those species which are common to most of the districts of the London Clay, 

 particularly the two most common species of Xantkopsis. The genera Mithracia, 

 Xanthilites, Playiolophus, Portunites, (Edisoma, Campylostoma, and Goniochele, and the 

 Macrurous genus Scyllaridia are, as far as I have observed, confined to this zone. There 

 is one species, Cyclocorysler pidchellus, which has hitherto occurred only in the third zone, 

 a single specimen having been found at Holloway. Hoploparia gammaroides is far more 

 numerous at Sheppey than in either of the other localities, but it also occurs in the 

 Highgate and Holloway districts. Hoploparia Bettii, on the contrary, is far more numerous 

 in the North London than in the Sheppey zone, and appears to be equally common 

 to both the second and third zones of Mr. Prestwich. Finally, Archaocarabus BoioerbanJcii 

 is principally, but not exclusively, a Sheppey species ; a few specimens from Holloway 

 existing in Mr. Wetherell's collection. I subjoin a list of the species described in the 

 present work, with the localities in which they occur. 



Species. 



Sheppey, 



Heme Bay, and 



Southend. 



Highgate. 



Whetstone, 



Holloway, 



Hornsey, &c. 



Alum Bay. 



Bognor. 



Mithracia libinioides 



— 











Xanthopsis Leachii 



— 



— 





— 



— 



bispinosa 



— 



— 









unispinosa 



— 



— 









Xanthilites Bowerbankii . 



— 











Plagiolophus Wetherellii . 



— 











Portunites incerta . 



— 











(Edisoma amhiguum 



— 











Campylostoma matutiforme 



— 











Cyclocorystes pulchellus . 







— 







Goniochele angulata 



— 











Dromilites Lamarckii 



— 



— 



? 







Bucklandii 



— 



— 









Hoploparia gammaroides 



— 



— 



— . 







Bellii . 



— 



— 













Trachysoma scabrum 





— 









Thenops scyllariformis 



— 



— 











Scyllaridia Koenigii 



— 











Archseocarabus Bowerbankii . 



— 



1 



— 







The other districts in which the London Clay exists have not been hitherto examined 

 with any degree of care and diligence ; and it is probable that there are yet several 

 species which have not been discovered, and which will reward the researches of some 

 future investigator. 



