1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo 469 
however, destroy living vegetation and may thus occasionally become 
pests of some economic importance. The African Achatina fulica (Férus- 
sac), introduced into Ceylon about 1900, has become so abundant there 
as to be a serious menace to agriculture.! se aa 
Vegetarian mollusks show decided preferences in the choice of their 
food, as is well known to all who have to deal with them as pests in 
gardens. In nature certain plants appear to be adequately protected 
against their depredations and Stahl has written a suggestive account of 
the various methods by means of which this is accomplished.? It is, 
however, difficult to accept Stahl’s contention that plant-eating mollusks 
are usually in a famished condition, because many plants are so effectively 
protected against their attacks. This view certainly fails to account for 
the prodigious numbers of vegetarian snails and slugs found in certain 
localities. Moreover, many snails and slugs are extremely partial to 
fungous food, even devouring without apparent harm fungi that are 
decidedly poisonous to man. Some slugs have a specialty of feeding on 
lichens, which they crop off from tree trunks.‘ 
It has been asserted that in some cases terrestrial mollusks are in- 
strumental in the pollination of certain flowers with openly exposed 
stamens and styles, the pollen adhering to the crawling snails and being 
thus carried upon the style. But whether there are flowers that could 
truly be called “malacophilous,”’ because they normally rely upon these 
animals for their pollination, appears somewhat doubtful.® 
The Streptaxide are all rapacious snails and perhaps the most 
important predaceous enemies of African land mollusks, although they 
occasionally attack also other soft-bodied invertebrates, such as earth- 
worms. In the ‘Review of Land Mollusks’ the senior author has called 
attention to the extraordinary development of that family in Africa, 
where it probably numbers more species than any other. ‘Terrestrial 
1Paravicini, EH, M.M. 1922. ‘Over schadelijke en nuttige weekdieren van tropisch Azié.’ Teys- 
mannia, XX XIII, pp. 24-28, Pl. 
Gibbons (1879, Journ. of Conchology, II, p. 148) has reported that Achatina panthera may excep- 
tionally become carnivorous. : 
2Stahl, E. 1888. ‘Pflanzen und Schnecken. Biologische Studie tiber die Schutzmittel der Pflanzen 
gegen Schneckenfrass.’ Jenaische Zeitschr. Naturw., XXII, pp. 557-684. . ; 
’Stahl’s views have been critically examined by Heikertinger, F. 1914. ‘Ueber die beschrankte 
Wirksamkeit der natiirlichen Schutzmittel der Pflanzen gegen Tierfrass.’ Biol. Centralbl., XXXIV, 
. 81-108. 
oe 4Elliott, W. T. 1923. ‘Some observations on the mycophagous propensities of slugs.’ Trans. 
British Mycol. Soc., VIII, pp. 84-90. ants : 
RAathay, E. 1898. ‘Ueber den ‘‘ Frass’”’ von Helix hortensis auf Baumrinden.’ Zeitschr. f. Pflanzen- 
krankh., VIII, pp. 129-133. 
5See Ludwig, F. 1891. ‘Die Beziehungen zwischen Pflanzen-und Schnecken.’ Beihefte z. Bot. 
Centralbl., I, pp. 35-39. ; 
Zaunick, R. 1916. ‘Die Befruchtung der Pflanzen durch Schnecken.’ Nachrichtsbl. Deutsch. 
Malakoz. Ges., XLVIII, pp. 74-91. ‘ 
Ehrmann, P. 1917. oO mur Frage der Bestéaubung von Bliiten durch Schnecken.’ Nachrichtbl. 
Deutsch. Malakoz. Ges., XLIX, pp. 49-75. 
