HISTORICAL SKETCH. XX111 



gona and Maerooyona are indiscriminately grouped; but with the 

 exception of the last named, which has good conchological peculiari- 

 ties, one would expect this ; for there are no diagnostic characters 

 of these super-generic groups to be found in the shells alone. 



The work of PfeifFer, although begun in the last period, extended 

 through the greater portion of this one. Final results of this great 

 series of monographs are given in the Nomenclator Heliceorum 

 Viventium, edited by Clessin (1878). The system of classification 

 differs but little from that of Albers-Martens. 



The successive papers and volumes of Binney and Bland upon the 

 land shells of America, although based on Die Heliceen, have made 

 notable improvements in the treatment of cis-Atlantic groups, 

 largely the result of Binney's work upon the jaws and radulae of 

 United States and West Indian species. The work of Tryon upon 

 Helices has been based upon conchological studies only, and is 

 essentially a modified form of the Albers-Martensian. Fischer like- 

 wise gave no weight to anatomical characters in his treatment of 

 Helices. 



The systematic work of Morch, although begun in 1859 (Mai. Bl. 

 vi, 109), belongs to this epoch rather than the last. Fully recogniz- 

 ing the unreliability of groupings based upon shell-contour, he pro- 

 poses to use the jaw as a basis for dividing land snails into primary 

 groups. The arrangement given is as follows, the genera of Helic- 

 idse being italicised: 



1. OXYUNATHA. Jaw with a projecting tooth, Liniax, Vitrina, 

 Succinea, Helicella, Zomtes,Leucochroa, Ryssota, Obba, Caracolla, 

 Otala, Pleurodonta. 



2. AULACOGNATHA. Jaw striated, with crenulated margin. E'ury- 

 omphala, Bradybcena, Sogda, Cochlicella, Rum in a, Pupa, Glaus- 

 ilia. 



3. ODONTOGNATHA. Jaw with separated cords which form teeth at 

 its margin, Arion, Ariolimax, Nanina, Teba, Pomatia,Helicogena, 

 Helicogona (Campy Isea), Achatina, Limicolaria, Bulimus. 



4. GONIOGNATHA. Othalicus, Pseudostrombus ( Liguus). 



5. AGNATHA. Oleacina, Testacella. 



In 1835 (Journ. de Conchyl.) this idea is further elaborated and 

 the Elasmognitha added.* As I have shown on a previous page 

 (xi), the jaw is as unreliable as the shell ; and the family groups 



