E. Wilson — British Liassic Gasterojjoda. 195 



otlier two divisions of the Lias, would reduce his gross total to 370. 

 Then again we find some of the genera repeated under different 

 names: 'Amberleya,' 'Eucyclus,' and ' Tectaria,' for example, are cited 

 as three instead of as one only, and similarly the synonymous 

 Act<xonina and Orthostoma are apparently counted as two. 



I have recently drawn up lists of the British Liassic Gasteropoda 

 which, exclusive of those now described, comprise 425 species, dis- 

 tributed provisionally under 51 genera. In these lists care has been 

 taken to avoid the reduplication of names, but it is probable that a 

 small number of the species have been counted twice under different 

 sj'nonyms. These last, however, will, I believe, be more than 

 balanced by the various new forms now awaiting description. The 

 number of genera on the other hand is almost certainly too great. 

 The 425 species are very unequally distributed among the genera. 

 The dominant Liassic genera are Trochus, Turbo, Ceritliium, and 

 Pleurotomaria. Taking with the last the sub-group Cryptcenia, each 

 of these genera would comprise about 50 species, or together nearly 

 a moiety of the whole number. Next comes Chemnitzia with some 

 30 species, and then Amberleya {^:zEucyclus) dceonina (= Ortho- 

 stoma), TurriteUa, and Patella, with from 10 to 16 each. The follow- 

 ing genera are represented by an average of 6 species each : Actceon 

 (= Tornatella), Alaria, Dentalium, DiscolieHx, Eulima (= Niso), 

 Litiorina, Naiica, Neritopsis, Phasianella, Pitonillus (= Rotella), 

 Solarium, Straparolus and Trochotoma ; whereas Cylindrites, Crypt- 

 aiilax, Delphinulaf, Euomphalusf, Kilvertia (:=Exelissa), Monodonta, 

 Nerita, Neritina, Oiiustns, Purpurina, Rimula and Rissoa are repre- 

 sented by 1 to 3 species each only. The remaining genera, which are 

 mostly founded on extremely few forms, and in some cases on single 

 and imperfect or on minute and immature specimens, cannot be con- 

 sidered to be satisfactorily established at present. These are Chiton, 

 Conns, Fusus, Nerincea, Pterocera, and Pyrula, one if not both of 

 Moore's genera Pleuratella and Pterocheilos, and the following 

 terrestrial and freshwater types : — Ampullaria, Helix, Hydrobia, 

 Melania, Planorbis, Proserpina, Valvata, and Vertigo. Some of the 

 foregoing are pi'etty sure to break down as Liassic genera under closer 

 scrutiny and the acquisition of more satisfactory material. Indeed, 

 it is very questionable whether any one of the first six of the above 

 genera can be maintained; and, before accepting any land or fresh- 

 loater form, as coming from a formation so essentially marine as the 

 Lias, we must require in each case the most clear and convincing 

 evidence. The net result of a future revision will probably be to 

 reduce the number of generic types given above, whereas the species 

 are probably capable of an appreciable and immediate increase. 



The enumeration of 425 species of British Liassic Gasteropoda in 

 1886 as compared with the trivial number of six only in 1854, is a 

 striking illustration of the progress which has been made in Palteon- 

 tology in this country during the last thirty years. 



Without further preface, I proceed to the main object of the present 

 communication, which is to describe thirteen species of Gasteropoda. 

 These are mostly new to science, and all are new to the British Lias. 



