COLIMACEA. 85 



XIII, p. 341 and 511 ; Thompson, Ann. and Mag. Nat. Hist., 

 VI, p. 34; Rossraassler, VIII, p. 37, pi. 39, f. 531, var.; 

 Brown, Illust. Conch., p. 53, pi. 18,* f. 7, 8; Helix vitrea, 

 Brown, Edin. Journ. Nat. and Geo. Science, I, p. 12, pi. 1, f. 

 12, 13, 14; Zonites crt/stallinus, Leath, Moll., p. 105. 



Shell thin, depressed, of a very glossy, crystalline, greenish- 

 white colour ; spire with five well defined, gradually decreasing 

 volutions, terminating in an extremely small, hardly-raised 

 apex ; base of the shell a little convex, provided with a small, 

 but deep umbilicus ; aperture semi-lunate, and enveloping the 

 body. Diameter three-sixteenths of an inch. 



This species may at once be distinguished from its con- 

 geners, by its extremely glass-like aspect, the number of its 

 volutions, and in the body one being but little thicker than the 

 lower volution of the spire. 



The H. cri/stallina Ts not uncommon in many parts of Eng- 

 land. It was first found in Scotland by my esteemed friend 

 James Gerard, Esq., who detected it in an old wall at Corstor- 

 phine Hill, near Edinburgh ; where I afterwards found it. 

 Thompson says it is generally distributed in Ireland, occurring 

 in moss, under stones, and upon decaying wood, both in wet 

 and dry situations. He adds, " Some adult specimens which I 

 have collected have had but three and a half volutions, instead 

 of four and a half or five, the ordinary number." I have great 

 doubts of these last mentioned being really the II. crystallina, 

 as one of its strongest characters is, the number of its volutions, 

 in which it is only equalled by the following species. 



37. Helix excavata, pi. IX, f. 13, 14. 



Helix excavata, Bean; Alder, Cat., p. 13, No. 53; lb., Mag. 

 Zool. and Bot., II, p. 107; Thompson, Ann. and Mag. Nat. 

 Hist., VI, p. 34; Brown, Illust. Conch., p. 53, pi. 18,* f. 9, 10; 

 Helix lucida, var., Turton, Man., p. 57, pi. 4, f. 39 ; Helix 

 nitida, Jeffreys, Linn. Tr., XIII, p. 339 and 511. 



Shell subglobose, transparent, diaphanous, shining, yellowish 

 horn-coloured, and covered with longitudinal, irregular wrin- 

 kles ; body very large ; spire subdepressed, small, consisting of 

 four or five well rounded, close-set volutions, terminating in an 

 obtuse apex ; base considerably inflated, and provided with a 

 large and deep umbilicus, in which may be seen the inside of 



