118 MALACOZOA. GASTEROPODA. PULMOBRANCHIATA. 



same time, all these shells differ much less from each other 

 than the varieties of Limnaeus pereger. 



First found by Miss Marion Macgillivray in a ditch at Ban- 

 ner Mill, near Aberdeen, where it exists in great profusion, 

 among Ranunculus aquatilis, and other plants ; afterwards 

 by Miss Isabella Macgillivray. 



Planorbis spirorbis. Muller, Verm. Terr, et Aquat. 161. Plan- 

 orbis spirorbis. Mont. Test. Brit. 455. PI. 25. f. 2. Planorbis 

 vortex. Var. B. Drap. Moll. Terrestr. et Aquat. 44. PI. 2. f. 6,|7. 

 Planorbis spirorbis. Flem. Brit. Anim. 277. Planorbis spirorbis. 

 Gray's Turton, 268. PI. 8. f. 98. 



2. Planorbis contortus. Contorted Coil-Shell. 



Shell widely and slightly concave above, with six nearly 

 equal, narrow, distinctly striated volutions ; the last rounded, 

 leaving a wide and deep cavity beneath, exposing part of all 

 the other whorls ; mouth narrow, semilunar ; colour light 

 brown, glossed or bronzed. Diameter nearly two-twelfths, 

 height one-twelfth. 



This, the smallest British species, is very abundant in pools, 

 ditches, rivers, and brooks. Its actions are in all respects 

 similar to those of the species described above. In advancing 

 in the water, it extends its foot, which is elliptical, depressed, 

 scarcely a twelfth of an inch in length, and moves regularly 

 and continuously onwards, but also at intervals exhibits the 

 sudden jerking motion above mentioned. The foot is of a 

 dusky brown colour ; the neck and head are black, the latter 

 projecting with a rounded extremity. The tentacula, longer 

 than the foot, are setaceous, a little dilated at the base, taper- 

 ing to a fine point, and a dusky grey colour ; the eyes black, 

 on the dilated base of the tentacula internally. The shell is 

 generally kept in the normal position, nearly horizontally, a 

 little declined to the right; but the animal can raise it con- 

 siderably. It advances on the surface, in the manner described, 

 keeping the shell horizontal. On land, it creeps in the same 

 manner ; but should the shell be turned round by twisting the 

 neck, it can proceed equally well with it in that manner. It 

 lives habitually among the roots, stems, and leaves of aquatic 

 plants. 



First found by Mr. John Macgillivray in a pool in the Old 

 Aberdeen Links, in May, 1841 ; in May, 1842, by Mr. Leslie, 

 in a small pond in the garden of the Professor of Medicine of 

 King's College, where it is very abundant on the grass and 



