Lymn-«a. 



MOLLUSCA. 



97 



1. Lymn^a pyramidalis The Pyramidal Lymnaea, pi. 



XL VI. fig. 1,2. 



Lymnrea pyramidalis. Brard ; Ann. du Mus. XV. pi. 24, 

 fig. 1, 2. Deshayes, II. p. 05, pi. 10, fig. 14, 15. Sowerby, 

 VI. p. 53, pi. 528, fig. 3. Fleming, p. 276. Brown, Elements 

 Fossil Conchology, p. 59, pi. 4, fig. 13. 



Elongated, subcylindrical; body large; spire pyramidal, small, 

 with five inflated, well defined volutions, the apicial one acute ; 

 aperture oblong, half the length of the shell, a little contracted 

 above, and rounded below ; outer lip sharp on the edge, and 

 but slightly expanded ; callus on the columella, with a shallow, 

 faintly defined furrow in its centre. 



Fresh Water formation, Headon Hill, Isle of Wight. 



2. Lymn^a maxima. — The Great Lymna>a, pi. XLVI. 

 fig. 3, 4. 



Lymneea maxima. Sowerby, VI. p. 53, pi. 528, fig. 1, 1. 

 Fleming, p. 276. 



Oblong-ovate, subcylindrical ; body large, and slightly inflated ; 

 spire a little pyramidal, with five moderately convex volutions, 

 terminating in an obtuse apex ; aperture oblong, a little con- 

 tracted above, and rounded below, occupying about half the 

 length of the shell ; outer lip thin ; columellar lip but slightly 

 reflected. 



Fresh Water formation, Isle of Wight. 



3. Lymn^a minima. — The Least Lymnrea, pi. XLVI. fig. 

 5, 6, 7. 



Lymneea minima. Sowerby, II. p. 156, pi. 169, fig- 1. 

 Fleming, p. 276. 



Oblong-oval, convex, smooth ; body large ; spire small, with 

 four rather inflated volutions, terminating in an acute apex; 

 aperture elongated, contracted and pointed above, and slightly 

 straitened below, occupying half the length of the shell. Length 

 a little more than a quarter of an inch. 



Fresh Water formation, Isle of Wight. 



4. Lymn;ea longiscata The Lengthened Lymnaea, pi. 



XLVI. fig. 8, 9. 



Lymneea longiscata. Sowerby, IV. p. 57, pi. 343. Fleming, 

 p. 276. Limneus lungiscatus? Brongniart, Mem. sur dcs Terr, 

 p. 16, pi. 1, fig. 9- Ann. du Mus. XV. pi. 22, fig. 9. 



Elongated, smooth, shining, with regular lines of growth ; 

 body large ; spire of medium length, with six or seven broad, 

 oblique, slightly inflated volutions, ending in an acute apex; 

 aperture ovate, elongated, occupying two-fifths the length of 

 the shell, contracted and acute above, and rounded below; outer 

 lip thin-edgod; pillar lip broad, obtuse at the edge, with a shal- 

 low twisted plait. 



Upper Fresh Water formation, Headon Hill, Isle of Wight. 



5. Lymnjea fusiformis The Spindle-shaped Lymna;a, 



pi. XL VL fig. 10, 11. 



Lymneea fusiformis. Sowerby, II. p. 155, pi. 169, fig. 23. 

 Fleming, p. 276. 



Subfusiform, smooth, and shining ; body large, slightly inflated ; 

 spire small, pyramidal, with five rather flat-sided volutions, the 

 apicial one acute; aperture elongated, narrow, slightly contracted 

 above, and rather rounded below, occupying about half the 

 length of the shell ; entire surface coverod with rather sharp, 

 regular lines of growth. 



Fresh Water formation, Isle of Wight. 



6. Lymn^a columellaris. — The Columellar Lymnaea, 

 pi. XL VL fig. 16, 17. 



Lymneea columellaris. Sowerby, VI. p. 53, pi. 528, fig. 2. 



Oblong-ovate, smooth ; body very large ; spire short, with 

 four inflated volutions; aperture oblong, wide, occupying about 

 half the length of the shell, contracted above, much expanded 

 and rounded below ; outer lip thin, ample ; inner lip with a 

 broad, greatly twisted, thick columella. 



The shortness of the spire will readily distinguish this from its fossil 

 congeners. 



Fresh Water strata, Hordwell Cliff. 



Genus LIL— PLANORBIS.— Mw/Zer. 



Shell discoidal, umbilicate ; spire and base depressed ; 

 apex always distinct; the volutions turning nearly on the 

 same plane, from right to left, so that when the spire is 

 held upwards, and the aperture next the observer, it is 

 situate on the left hand side; volutions ventricose, in 

 many species, often carinated, either above or below ; 

 aperture entire, obliquely semilunate, its length and 

 breadth being nearly equal, but broader than long in 

 some instances ; outer lip sometimes thickened ; umbili- 

 cus very wide ; destitute of an operculum. 



1. Planorbis obtusus The Obtuse Planorbis, pi. 



XLVLfig. 12, 13. 



Planorbis obtusus. Sowerby, II. p. 91, pi. 140, fig. 3. 

 Fleming, p. 279. 



Depressed, discoidal, smooth, pellucid, and shining; volutions 

 few, greatly concealed, embracing; aperture oblique, obtuse, 

 subcordiform. 



Fresh Water formation. Isle of Wight. 



2. Planorbis hemestoma — The Red-mouthed Planorbis, 

 pi. XLVI. fig. 18, 19, 20. 



Planorbis hemestoma. Sowerby, II. p. 91, pi. 140, fig. 6. 

 Fleming, p. 279- 



Discoidal, depressed, smooth ; volutions partly concealed ; 

 spire convex, umbilicate; base flat; aperture subtriangular, ob- 

 lique. Diameter one line ; thickness the fourth of a line. 



Plastic Clay, Plumstead. 



3. Planorbis cylindricus The Cylindrical Planorbis, 



pi. XLVI. fig. 21, 22. 



Lymiura cylindricus. Sowerby, II. p. 90, pi. 140, fig. 2. 

 Fleming, p. 279. 



Cylindrical ; three or four adpressed volutions, with concen- 

 tric, and obscurely elevated, stritc on the left side ; aperture 

 transverse, oblong, quadrangular, the angles obtuse, its width 

 exceeding its length, but without any indentation from the 

 second volution. Diameter nearly three times its thickness. 



Fresh Water formation, Isle of Wight. 



4. Planoriiis Lens. — The Lens-shaped Planorbis, pi. 

 XLVL fig. 26, 27. 



Planorbis Lens. Sowerby, II. p. 91, p'. 140, fig. 4. I'le- 

 ming, p. 279. 



Lenticular, flat, equally concave above and below, subcari- 

 nated, with embracing volutions; aperture subcordate, and very 

 oblique. Thickness about equal to a sixth of its diameter. 



Fresh Water formation. Isle of Wight. 

 2 B 



