MALACOZOA. GASTEROPODA. PULMOBRANCHIATA. 93 



gularly increasing, the last not proportionally larger ; the 

 umbilicus of moderate width, and deep ; the aperture ob- 

 lique, semilunar, wider than long. Diameter nearly a twelfth 

 and a quarter, height a third less. 



Animal with the foot and neck white, with a tinge of lilac, 

 the tentacula purplish ; the hind part of the body of a pale 

 reddish tint, which appears through the shell. 



The brilliant gloss, and delicate, clear, glassy transparency 

 of the shell of this species, distinguish it from all the others. 



First found by me among moss and grass, and around 

 the stumps of felled trees, in moist places, in Seaton Haugh, 

 on the 23d, and 27th of June, 1842. In September, found by 

 Mr. Leslie, near Inverury and in the Parish of Cluny ; by Miss 

 Macgillivray at Banff, Gamrie, Auchmedden, and other 

 places along the northern coasts. 



Helix crystallina. Muller, Venn. Terrestr. et Aquat. 11. 23. — 

 Helix crystallina. Drap. Moll. 118. PI. 8. f. 13, 14, 15, 16, 17. 

 — Helix crystallina. Jeffreys, Linn. Trans, xiil. 341, — Helix 

 crystallina. Flera. Brit. Anirn. 262. — Zonltes crystallluus. Gray's 

 Turton, 176. PI. 4. f. 42. 



9. Zonites fiiscus. Aletnhranous Zone-Snail. 



Shell suborbicular, depressed, slightly convex above, ex- 

 tremely thin, being quite membranaceous, flexible, ti'anspa- 

 rent, glossy, and very strongly wrinkled ; of five spiral turns, 

 of which the last is proportionally larger ; the suture deep, 

 the turns being considerably roimded toward the margin ; the 

 aperture large, oblique, roundish-lunate ; imibilicus very small, 

 encroached upon by the thin inner lip ; the colour greenish- 

 hyaline or pale greenish-brown. Diameter four-twelfths of an 

 inch, height as one to two. 



The animal, unlike that of Vitrina, can retreat Avithin the 

 shell as far as that of a Zonites or Helix, leaving a large space 

 vacant. It is of a pale greenish-grey, and the shell is so 

 transparent that the pulsations of its heart are distinctly seen 

 through it. It resides among moss, nettles, or other herbage in 

 small recesses on banks. 



When we consider that some species of Helix, and in parti- 

 cular Helix aspersa, H. arbustorum, and H. hortensis, often 

 occur in a semimexiibranaceous state, we might reasonably 

 suppose that the Zonitae, which are m\xch thinner, might 

 present individuals perfectly membranaceous, and thus might 

 be led to imagine the shells here described as merely unde- 

 veloped individuals of some species ; but no Zonites found 



