THE JAW IN PULMONATA 



211 



circular bites inflicted by a schoolboy upon his bread and butter. 

 The jaw of Helix (Fig. 107, B) is arched in shape, and is 

 strengthened by a number of projecting vertical ribs. That of 

 Limax (A) is straighter, and is slightly striated, without vertical 

 ribs. In Bulimulus (C) the arch of the jaw is very conspicuous, 

 and the upper edges are always denticulated ; in Orthalicus there 

 is a central triangular plate with a number of overlapping plates 

 on either side ; in Suceinea (E) there is a large square accessory 

 plate above the jaw proper. The form of the jaw is peculiar not 



Fig. 107. —Jaws of 

 various Pulmon- 

 ata : A, Limax 

 {g agates Drap., 

 Lancashire, 15); 

 B, Helix {acutis- 

 sima Lam., Ja- 

 maica, X 15) ; C, 

 Bulimulus (de- 

 pictus Reeve, 

 Venezuela, x 20) ; 

 D, Achatina 

 (fulica Fer., Mau- 

 ritius, X 7) ; E, 

 Suceinea (elegans 

 Eiss., Aral Dis- 

 trict, X 30) ; F, 

 Limnaea (stag- 

 nalis L., Cam- 

 bridge, X 30). 



only to the genus but to the species as well. Thus the jaw of 

 H. aspersa is specifically distinct from that of H. pomatia, and 

 that of H. nemoralis is distinct from both. Wiegmann has 

 observed ^ that in young Arion^ Limax^ and Helix^ the jaw con- 

 sists of two pieces, which coalesce by fusion in the adult, thus 

 indicating a stage of development in advance of the double jaw 

 which is found in most of the non-pulmonate Mollusca. In all 

 fresh-water Pulmonata there are two small accessory side plates 

 besides the jaw proper (Fig. 107, F). 



Nearly all the non-carnivorous Prosobranchiata, land, fresh- 

 water, and marine alike, are provided with two large lateral jaws. 

 1 Jahrb. Deut. 3Ialak. Gesell. ill. p. 193. 



