280 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



might easily have been derived fiom that occurring in Truncatellina ; 

 and the resemblance of the radula of this genua to the type found in 

 Punctum should probably be regarded as due to convergence. The 

 cusps of the teeth in two English specimens of Columella edentula 

 were not observed to have the blackish colour that Dall states he 

 found in some American examples.^ 



Summary. 



A study of Dr. Boycott's preparations shows that the penis is 

 very commonly entirely absent in Vertigo pusilla, Miill., F. suhstriata 

 (Jeffr.), F. alpestris, Alder, F. moulinsiana (Dupuy), and Truncatellina, 

 britannica, Pilsbry, although it has been found in a few specimens of 

 the last three species, as well as in Vertigo pygmcea (Drap.), F. 

 antivertigo (Drap.), and Columella edentula (Drap.). The specimens 

 without a penis are fully developed in other respects, with 

 spermatozoa as well as ova in the hermaphrodite gland ; the part of 

 the vas deferens near the oviduct is usually present, but it ends 

 blindly. 



A classification of the British Vertigininse based on the genital 

 organs agrees well with that founded on the shell, although the radula 

 of F. moulinsiana suggestar that this species stands slightly apart 

 from the other members of the genua Vertigo. The reproductive 

 organs of Truncatellina differ in some respects from those of Vertigo, 

 and the male organs (when present) resemble those of the genus 

 Columella. No evidence has been found in support of Lehmann'a 

 statements that flagella occur in various species belonging to these 

 three genera ; on the other hand, Hanna's views about the simplicity 

 of the male organa of Columella edentula, and the affinities of this 

 animal with Vertigo rather than Punctum, are confirmed. 





THE PRESENCE OE A SUB-CEREBRAL COMMISSURE IN THE 

 ORTHURETHRA. 



By Hugh Watson, M.A. 



Bead 11th May. 1923. 



The cerebral nerve-ganglia might be termed the brainiest part of 

 a mollusk, and the commissures that unite these two ganglia are 

 structures of considerable importance. For if the chief nerve- 

 centres on the right and left sides were not directly connected with 

 each other, it is 'difficult to perceive how an animal could efficiently 

 regulate its actions to achieve definite ends. To be double-minded 

 is to be .unstable in all one's ways. 



It is well known that in the most primitive order of Gastropods, 

 the Aspidobranchia, the cerebral ganglia are directly connected by 

 two commissures, one passing above the buccal mass and the other 



1 Proc. U.S. Nat. Mus., vol. xli, 1912, p. 372. 



