GASTEROPODA. 9 



ment (not yet satisfactorily adjusted) has existed among conchologists as to the 

 correct determination of the upper and under sides of these shells ; some have con- 

 sidered them as dextral, while others maintained them to be sinistral ; in my descrip- 

 tions they are considered as dextral, although the artist has made them sinistral. 



1. Planoebis complanatus. Linn. Tab. I, fig. 10, a — c. 



Helix complanata. Linn. Syst. Nat. p. 1242, 1766. 

 Planorbis umbilicatus. Mull. Verm. p. 160, No. 439, 1774. 

 Helix complanata. Mont. Test. Brit. p. 450, t. 25, fig. 4, 1803. 

 Planorbis complanatus. Flem. Brit. An. p. 278, 1828. 

 Planorbis marginatus. Drap. Moll. p. 45, pi. 2, fig. 11-12, 1805. 



— Gray. 2d edit. Turt. Man. p. 265, fig. 88, 1840. 



— S. Wood. Catalogue 1842. 



PL Testa discoided, complanata, laevigata-, anfractibus swperne convexis, in/erne 

 coiitplanatis : carina marginali, non prominenti ; spird depressd. 



Shell discoidal, flattish, smooth, with the spire slightly depressed ; nearly flat 

 beneath, with the margin carinated but not prominent ; volutions convex above . 

 aperture lunate ; the upper part of the peritreme projecting beyond the lower. 



Diameter, f of an inch. 



Locality. Red Crag, Butley. 



Mam. Crag, Bulcham. Recent, Britain. 



My cabinet contains but one specimen of this species, found by myself in undis- 

 turbed Red Crag. It corresponds with the common recent form of this shell, and has a 

 slightly carinated edge on the flat or lower side, while the volutions on the other 

 side are convex, with the spire depressed and concave, and the edge of the outer lip 

 projecting and curved. Two specimens from the Mam. Crag, near Norwich, were 

 sent to me for description by Mr. Wigham ; they do not differ, however, in any 

 respect from my own. 



2. Planorbis spirorbis. Midi. Tab, I, fig. 11, a — c. 



Planorbis spirorbis. Mull. Verm. 11, p. 161, 1774. 

 Helix spirorbis. Gmel. Syst., p. 3624, No. 36, 1788. 



— Mont. Test. Brit. p. 455, t. 25, fig. 2, 1803. 

 Planorbis vortex, var. /3. Drap. Moll. t. 2, fig. 6-7, 1805. 

 Planorbis spirorbis. Gray. 2d edit. Turt. Man. p. 268, fig. 98. 



— S. Wood. Catalogue 1842. 



PL Testa diwoidea, utrinque plano-depressd ; anfractibus subcylindraceis, ultimo obsolete 

 angulato. 



Shell discoidal, thin, fragile, somewhat concave on both sides, with very slightly 

 increasing, subcylindrical or subquadrate volutions ; outer or lower margin obso- 

 letely angulated. 



Diameter, \ of an inch. 



Locality. Mam. Crag, Bulcham. Recent, Britain 



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