STROBILOPSIDiE. 3 



the acceleration or early appearance of apertural armature in 

 Tomatellinidae, Orcula, Lauria and Strohilops has been inde- 

 pendent in the four groups, and is not indicative of direct 

 relationship between any of them. 



On the whole, I am inclined to rank the Strobilopsidse as a 

 family, distinguished chiefly by characters of the shell. 



In the course of my work on the super-family Orthurethra 

 in this Manual, the problem of defining family groups has 

 constantly been before me. The partial solutions offered have 

 not been wholly satisfactory to myself. The difficulties have 

 been stated lucidly by Hugh Watson (Proc. Malac. Soc. Lon- 

 don XIV, pp. 20-27; diagram on p. 25). He has called atten- 

 tion to the fact that a division of the Orthurethra based on 

 any single character (such as the presence or absence of penial 

 appendix or flagellum, single or forked penial retractor, pres- 

 ence of a diverticulum of the spermathecal duct, degree of 

 elongation of the shell, etc.) would not accord with a division 

 based upon any other characters. At present the relative 

 value of these characters appears in most cases to be uncer- 

 tain. That some forms have been simplified secondarily seems 

 highly probable. Watson proposed that the Partulidse and 

 Achatinellidee (including Tomatellinidaj as a subfamily) be 

 retained as families, all the rest of the Orthurethra to be in- 

 cluded in Pupillidffi under a number of subfamilies. He does 

 not recognize characters of the shell as significant for family 

 grouping, though the construction of his diagram appears to 

 show that he relied upon them for his subfamily grouping. 

 Steenberg, whose work, fitudes sur 1 'Anatomic et la Systema- 

 tique des Maillots, 1925, is the most important document we 

 have on PupiUid anatomy, would divide the Orthurethra into 

 sixteen families. 



Although the meaning of characters of the shell may be- 

 come vague or illegible by degenerative changes, convergent 

 evolution and the like, I am inclined to believe them somewhat 

 more stable than the details of genitalia in these Orthurethra, 

 and to utilize them in grouping the genera into families. To 

 rank the Amastridse, the Cochlicopidge or even the Strobilop- 

 sidse as subfamilies of Pupillida does not seem to me to clarify 



