122 Annals of the South African Museum. 



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

 instance. 



FAMILY ACAYIDAE, 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 nourished 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 Actaeonidae, 



the Chilinidae, and the Auriculidae, 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 



