MALACOZOA. GASTEROPODA. PECTINIBRANCHIATA. 139 



from young individuals of Littorina littorea by its having the 

 outline of the spire a little convex, the spiral turns more con- 

 vex, the suture deeper, the junction of the upper edge of the 

 last whorls coming off directly, and the outer lip consequently 

 forming a right angle, whereas in Littorina littorea it forms a 

 very acute angle, and by its inside being always of a deep 

 purple-brown colour. But it approaches very closely to some 

 of the varieties of Littorina rudis, of which, in fact, it is probably 

 only a variety, individuals occurring which might with equal 

 propriety be referred to either species. In its most charac- 

 teristic state, it differs from that shell, in being much thinner, 

 in having the spire longer, the whorls more convex, the last 

 much rounded, and without the angular band usually seen on 

 that of Littorina rudis above, and of Littorina saxatilis below. 

 First observed by me on an excursion with my class, on the 

 18th of July, 1841, in a small inlet or salt-marsh, near New- 

 burgh, on the Estuary of the Ythan, where it resides among 

 Poa maritima and Salicornia herbacea, near high-water mark, 

 and creeps about on the clayey mud, along with Rissoa Ulvse. 



Turbo tenebrosus. Mont. Test. Brit. 303. PI. 20. f. 3. Turbo 

 tenebrosus. Flem. Brit Anim. 298. 



5. Littorina petrcea. Smooth Periwinkle. 



Shell globoso-comcal, rather thin; with the spire shorter 

 than the last whorl, the apex obtuse ; the whorls very convex, 

 transversely rugoso-striate, the suture distinct; the mouth 

 roundish ; the peristome thin, the outer lip united at a rather 

 acute angle ; the exterior glossy black, often banded or varie- 

 gated with white ; the interior dark purple. Length three- 

 twelfths of an inch, breadth nearly the same. 



Nearly allied to Littorina saxatilis, but distinguishable by its 

 glossy surface, destitute of spiral striae. 



On the Kincardineshire coast at high-water mark. Among 

 shell sand on the beaches from Aberdeen to Fraserburgh. 



Turbo petrasus. Dillw. Rec. Shells. 820. Helix petraea. Mont. 

 Test. Brit. 403. Turbo petraeus. Flem. Brit. Anim. 298. Litto- 

 rina petraea. Johnst. Berw. Trans, iii. 268. 



6. Littorina Beanii. Bean's Periwinkle. 



Shell globoso-conical, obtuse, of three convex, rather thick 

 turns, separated by a moderately deep suture ; the last turn 

 very large, somewhat glossy, faintly striated transversely, with 

 hardly perceptible indications of longitudinal grooves, and 



