GASTEROPODA. 9 



(not )'Ct satisfactorily adjusted) has existed among concliologists 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. Lhm. Tab. I, fig. 10, a — c 



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

 Plaxorbis I'MBILICATUS. Miill. Verm. p. 160, No. 439, 1774. 

 Helix complanata. Mont. Test. Brit. p. 4.50, t. 25, fig. 4, 1803. 

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

 Planoebis makginatus. Brap. Moll. p. 4,'i, pi. 2, fig. 11-12, 1805. 



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



— S. Wood. Catalogue 1842. 



PL Testa discoided, complanata, Itsvigatd: anfractibus superne convexis, inferne 

 complanatis : carina marginali, nan jirominenti ; 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 difi"er, however, in any respect 

 from my own. 



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



Planokbis spiroebis. Mali. Venn. 11, p. 161, 1774. 

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



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



Planoebis voetex, var. /3. Braj}. Moll. t. 2, fig. 6-7, 1805. 

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

 — S. Wood. Catalogue 1842. 



PI. Testd discoidea, utrinque plano-dep)ressd ; anfractibus suhcylindraceis, ultimo obsolete 

 ancjtdato. 



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

 increasing, subcylindrical or subquadratc volutions ; outer or lower margin obsoletely 

 angulated. 



Diameter, \ of an inch. 



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



2 



