122 Annals of the South African Museum. 



two years ago in these Annals, they are omitted in the present 

 instance. 



Family ACAVIDAE, Pilsbry, 1900. 



Proc. Acad. Nat. Sci. Phila., p. 564. 



It is generally believed that millions of years ago a great southern 

 continent stretched westward from South Africa as far as the Andes, 

 and eastward through Madagascar and Southern India to the 

 Australian region. The climate of this continent was very cold 

 towards the end of the Carboniferous period ; but later it became 

 warmer, and the snails that dwelt there flourished exceedingly, 

 several new families being evolved. And one of these families 

 seems to have been the Acavidae. 



Now it is not difficult to form some idea as to what the first members 

 of the Acavidae were like ; for it is reasonable to suppose that they 

 would possess any primitive characters that are still retained by some 

 of their descendants, as well as such other features as are found in all 

 the modern members of the family, or at least in all the more archaic 

 genera. We may suppose, therefore, that the eggs of these snails 

 would be larger than usual, and that the animals themselves would 

 be above the average size. The shell would have a pointed spire 

 and laterally compressed whorls ; that is to say, both the shell and 

 its aperture would be higher than broad. This is the form of shell 

 found in the most primitive Euthyneura, such as the Actaconidae, 

 the Chilinidae, and the Auricididae, as well as in many of the more 

 ancient families of the Stylommatophora, and it is still retained 

 by several members of the Acavidae. There would be the usual two 

 pairs of tentacles, and the labial lobes would be well developed. The 

 foot would have neither a definite peripodial groove nor longitudinal 

 grooves on the sole. No caudal mucous pore would be developed. 

 The lung would be rather short, and the pulmonary veins would 

 branch over the whole of its roof, the first branch of the pericardial 

 vein being nearly as large as the principal pulmonary vein. The 

 excretory system would be unusually simple, the kidney being broad 

 and probably without even a primary ureter. The nervous system 

 would be of the type found in most of the more primitive snails and 

 slugs, there being eleven separate ganglia. The cerebral ganglia 

 would probably be rather near together, but the connectives uniting 

 them with the remaining ganglia would be long. The jaw would be 

 without ribs, but would probably have faint vertical striae and a 



