AGNATHOMORPHA. XI 



presence of a jaw. The lung (pi. 52, fig. 6, C. Vancouver ensis) - 

 has no noticeable venation except the pulmonary vein. The 

 oblong kidney is longer than the pericardium, lying parallel 

 to it. The gut ureter is closed throughout. The genital ori- 

 fice is submedian, below the pneumostome. Spermatheea on 

 a long duct, arising from the long vagina; epiphallus long. 

 Genera Circinaria, Scolodonta. 



The position of Scolodonta is somewhat uncertain, but at 

 least one species has been shown to have a jaw. There are 

 various degrees in the degeneration of the jaw in carnivorous 

 snails, so that the value of this character is not great. As yet 

 we know so little of the anatomy of South American Helicoid 

 Streptaxida that the limits of the Streptaxidce and Circinar- 

 iidce are uncertain. 



Family APERID^E. 



This family contains a single South African genus of 

 several species, none of them yet thoroughly described ana- 

 tomically. It may prove to be more nearly related to the 

 Rhytididce than to other Agnathomorph or Agnathous fami- 

 lies. Genus Apera Heynemann (Chlamydephorus Binney, 

 preoc. Vol. I, p. 17) . 



Family RHYTIDID^E Pilsbry. 



This family is restricted to South Africa, Australia, New 

 Zealand, New Caledonia, and neighboring islands of the 

 "Melanesian plateau." Schizoglossa has a degenerate, Dau- 

 debardia-likQ shell, and much modified soft anatomy. Other 

 genera have the shell Planorboid or Helicoid. The lung is 

 rather short with distinct venation (pi. 52, fig. 1, Natalina 

 knysnaensis) . The reflexed ureter (fig. 1, r. u.) runs back 

 to the base of the lung ; thence a thickened band but no closed 

 secondary ureter accompanies the last fold of the intestine. 

 The shape and position of the kidney are as usual in Holopoda. 

 Genera: Schizoglossa, Paryphanta, Natalina (Aerope, preoc.), 

 Rhytida, Rhenea (El&a, preoc.), Diplomphalus, and probably 

 Coxia. 



