VALLONIA. 343 



Pupa, bearing two minutely crenulatcd lappets, which hang down on cither 

 side of the month like a visor, reminding one of tlie oblique folds on the 

 head of Glandina trimcata, which we believe to be homolo- 



Pii? 226 



gous to them. A longitudinal furrow extends from the 

 mouth downward. The body is so translucent that when 

 extended the ganglionic centres can be plainly seen. In 

 motion it is exceedingly graceful, at times poising its 

 beautiful shell hio;h above its body, and twirling it around, Ammai of 



"^ . ;' . =• ' Helix harpa. 



not unlike the Physa, again hugging its pretty harp close 

 to its body; the shell, when in this last position, continually oscillates, as 

 if the animal could not balance it ; it rarely ever moves in a straight line, 

 but is always turning and whisking about, and this is done at times very 

 quickly and abruptly. (Morse.) 



Jaw and lingual membrane (see above). 



The species is said by Mr. Morse to be viviparous. 



VALLONIA, Risso. 



Animal heliciform (see Bost. Journ. Nat. Hist., I. PI. IX. Fig. 2) ; other 

 characters as in Patula. 



Shell umbilicated, depressed, diaphanous, whorls 3^ - 4 ; aperture oblique, 

 subcircular ; peristome white, thickened, reflected, its margins contiguous or 

 convercrinoc. 



The single known species is circumpolar, common to the three continents. 

 In North America its range is shown below (p. 344) ; in Europe it is found 

 everywhere, reaching indeed Northern Africa, the Azores, Madeira, etc. ; in 

 Asia it occurs in Siberia, Thibet. This wide distribution, so unusual in the 

 land shells, suggests great antiquity for the species. It is said to have been 

 found in the Red and Norwich Crag (see Prestwich, Quart. Journ. Geol. 

 Soc, XXVII. 493). 



Jaw low, wide, slightly arcuate, ends but little attenuated, blunt ; cutting 



margin without median projection ; anterior sur- 

 ^^ ^. ^ __ Z 2:r^ face with numerous crowded, broad ribs, den- 



X^^AJSS^mllj^^::^ ticulating the lower margin (Fig. 227). 



^^<-^ Lingual membrane (PI. VII. Fig. U") Ions 



Jawof r.pw2cAc^/a(Mor8e). , ° ^. o y o 



and narrow, arranged as in Patula, Morse gives 



73 rows of 11 — 1 — 11 teeth, with 3 perfect laterals. I counted 10 — 1 — 10, with 

 3 perfect laterals. Centrals with the base of attachment long and narrow, ex- 

 panded and notched at the outer lower angles, narrowed above and reflected ; 

 reflection very small, tricuspid, all the cusps bearing very short cutting points, 

 the central one, as usual, longest. Laterals with the base of attachment twice 

 as broad as in the centrals, the inner lower angle suppressed, notched at the 

 outer angle, broadly reflected above ; reflection larger than in the centrals, 

 with one inner, long, slender cusp, reaching nearly the lower edge of the base 



