990 Mr. E. A. Smith on the Genus Paludina. 
Kirk as occurring in the New-Zealand seas; but I am in- 
clined to think the New-Zealand species distinct, since Mr. 
Kirk mentions the existence of a ‘‘ prominent spine’ on the 
anterior margin of the hand in his specimens: this I have 
never observed in the true P. pusillus, which has the distal 
end of the anterior margin acute or armed with a very small 
spinule. 
Atelecyclus rotundatus, Olivi. 
Several specimens of this common Mediterranean species are 
in the collection. Length of the largest 11 lines (23 millim.), 
breadth a little over I inch 1 line (28 millim.); the others 
are all much smaller. 
[To be continued. | 
XXI.—Remarks upon Mr. Wood-Mason’s Paper “On the 
Discrimination of the Sexes in the Genus Paludina.” By 
EpGcar A. SMITH. 
Mr. Woop-Mason’s object is to show that the sexes of 
Paludina are distinguishable by differences both in the shells 
and animals. ‘This fact, I need scarcely remind the readers 
of this journal, has been known for nearly two hundred years. 
Lister, in 1695 *, gave a very fair anatomical description of 
the animal, demonstrating (p. 46) the bisexuality of the 
genus and the characters of both male and female. 
He says, in reference to the distinguishing external features, 
‘¢ si tamen nota aliqua externa, qua mas a foemina primo intuitu 
discerni possit, desideretur, scire licet mares fere minores esse, 
deinde, in maribus dextrum cornu (tab. 2. fig. 1, f) sinistro 
duplo latius esse, apiceq. obtuso desinere.”” On turning to 
the above-quoted figure we find it thus described: —‘ Dextrum 
maris cornu obtusum, in quo penis exitus est.” 
The latter discovery has since received confirmation from 
Cuvier |, Moquin-Tandon {, and others. 
Supposing a marked difference in the size of the adult shells 
generally prevails in the sexes of Paludina, J fail to perceive 
how a conchologist, judging from the shells alone, can know 
which, in any series he may have before him, have contained 
males and which females. In any large number of a species 
* ¢Hxercitatio anatomica altera, in qua maxime agitur de Buccinis 
fluviatilibus et marinis’ (12mo, London, 1695). 
+ Ann. du Mus. 1808, p. 170; also Mémoires pour serv. a l’Hist. des 
Mollusques, 1817. 
{ Mollusques terr. et fluv. de France, 1855, vol. ii. pp. 5380-537. 
