GASTEROPODA. 9 



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

 determination of the upper and under sides of these shells ; some have considered them 

 as dextral, while others maintained them to be sinistral ; in my descriptions they are 

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



1. PLANORBIS COMPLANATUS. Linn. Tab. I, fig. 10, a c. 



HELIX COMPLANATA. Linn. Syst. Nat. p. 1242, 1766. 

 PLANORBIS TJMBILICATUS. 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. Drop. 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, complanatd, Icevigatd: anfractibus superne convexis, inferne 

 complanatis : 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., 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. Mull. 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 discoidea, utrinque plano-depressd ; anfractibus subcylindraceis, ultimo obsolete 

 angulato. 



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

 increasing, sub cylindrical or subquadrate volutions ; outer or lower margin obsoletely 

 angulated. 



Diameter, \ of an inch. 



Locality. Mam. Crag, Bulcham. Recent, Britain. 



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