20 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



For we have seen that whether we regard the locomotory or the 

 nervous system, the excretory or the digestive system, the muscular 

 or the reproductive system, all the evidence points to the same 

 conclusion. 



FAM.11.Y 'RELATIONSB.l'PS OF ACANTHTNULA, VaLLONIA, PaTULASTSA, 



AND Pyramidula. While it is easy to be certain that these four 

 genera belong to the Orthurethra, and have very little affinity 

 with the Endodontidae or the Helicidae, in the present imperfect 

 state of our knowledge it is very difficult to decide exactly where 

 they should be placed among the various orthurethrous families. 



Steenberg considers that Acanthinula and Vallonia are nearly 

 allied to each other, and he places them provisionally in a family 

 by themselves, which he names the Acanthinulidse, and which he 

 believes to be closely related to both the Enidse and the Pupillidae.^ 

 Now it is evident that Vallonia and Acanthinula are closely allied 

 genera. It is true that Acanthinula differs from Vallonia in the 

 higher spire, narrower umbilicus, and darker colour of its shell ; 

 in the smaller size and slightly larger number of the lateral teeth of 

 the radula ; ^ and also, when the male organs are developed, in the 

 shortness of the part of the penis in front of the penial appendix, 

 the presence of a pair of small fiagella on the epiphallus, and the 

 posterior origin of the penial retractor. These differences, however, 

 while quite enough to establish beyond doubt the generic distinctness 

 of Vallonia and Acanthinula, are not very much greater than those 

 that separate Acanthinula aculeata and A. lamellata,^ and would 

 certainly not justify the placing of the two genera in separate 

 families or even in separate sub-families. 



That Steenberg is also right in regarding these genera as closely 

 related to both the Enidae and the Pupillidse is abundantly clear 

 from the evidence that has already been put forward in this article. 

 But if the group which these genera form is to be regarded as a 

 distinct family, it would seem better to call it the Valloniidas rather 

 than the Acanthinulidee, inasmuch as the former name is^not only 

 shorter and derived from an older generic name, but has been in 

 use for nearly twenty years,^ whereas the name Acanthinulidse is 

 little more than two years old. 



Patulastra differs widely from Vallonia and Acanthinula in its 

 reproductive organs ; and while the fact that it is viviparous might 

 partly explain the absence of a penial appendix (as in Pyramidula ^), 

 this would not account for the complicated structure of the epiphallus 



1 Vidensk. Meddel. Dansk Naturh. Foren., vol. Ixix, 1917, p. 14. 



2 The other differences in the radula are extremely slight, the rounded 

 inner edges of the marginal teeth of Acanthinula, and the length of the 

 central tooth of A. aculeata, being somewhat exaggerated in Bowell's figures 

 (Proc. Malac. Soc. Lond., vol. xi, 1914, p. 158). 



3 See p. 29. 



* Pilsbry, Proc. Acad. Nat. Soi. Phila., 1900, p. 564. 

 5 See p. 16. 



