FAMILY NERITACEA. 203 



1. Neritina fluviatilis. River Neritina. 



Shell ; obliquely oblong-ovate, sobd, fulvous wbite, more or less 

 covered with a variously reticulated 

 net-work of blue-black or grey, spire r~7^ 



very short, obtuse, whorls three, the \Y /~^\ 



last considerably produced, aperture \^_^ ; 



transversely semilunar, columellar 

 area broad, callous, slightly concave. ^JzQ^ -^^^~~ 



Nerita fluviatilis, Linnaeus (1758), Sgst. Nat. .SpzstV' Mr\ 



ocl. 10. p. 777. fiSSP^ ^lyS£; 



Theodoxus Lutetianus, Montford (1810), Condi. ^qBF ^Jgfe^ 



Sgst. vol. ii. p. 351. 

 Neritina fluviatilis and Bcetica, Lamarck (1822), Anim. sans vert. vol. vi. 

 Nerita Prevostiana, Partsch (1828), C. Pfeiff. Deutsch. Moll. vol. iii. p. 49. 



pi. viii. f. 11 and 12. 

 Neritina variabilis, Hecart (1833), Mem. Soc. Agr. Valenc. vol. i. p. 146. 

 Neritina thermalis, Boubee (1833), Bull. Hist. Nat. p. 12. 

 Neritina Dalmatica, Partsch (1835), Sow. Conch. Illus. f. 57. 

 Nerita zebrina, Eeclviz (1841), Rev. Zool. Soc. Cuv. p. 341. 

 Nerita Mittreana, Recluz (1842), Rev. Zool. Soc. Cuv. p. 181 and 182. 

 Neritina Prevostiana, Dupuy (1851), Hist. Moll. vol. v. p. 593. pi. xxix. f. 2. 

 Neritina Bourguignati, Recluz (1852), Journ. Conch, p. 293. 

 Neritince Numidica, Peloponensis, meridionalis , intexta, Jordani, Sardoa, 



Maori, Hildreichii, trifasciata, Anatensis and Anatolica, auctormn. 

 Hab. Throughout Europe. Asia Minor. North Africa. (Adhering to 



stones or crawling on the gravelly bottom of rivers and streams. Also 



in warm springs.) 



The generic features of this little river mollusk are peculiar and 

 constant, but its specific characters are variable in the extreme, and 

 it has been named twenty times over. In form, the shell varies from 

 obliquely oblong to subglobose, and the painting, though generally 

 a pattern of network, is most protean. The animal is of a pale 

 flesh- colour, the upper parts being more or less mottled with brown, 

 and there is generally a dark band between the tentacles, which 

 are rather conspicuously edged with a dark line. The animal is but 

 little protruded beyond its shell, and withdraws itself instantly on 

 being touched. It is pretty generally diffused throughout Europe 

 and Asia Minor, passing into North Africa. In Britain, it appears 

 chiefly in the south-western and eastern counties of England and 

 Ireland. Unlike the rest of our freshwater mollusks, the genus does 

 not occur in the Middle and Northern United States of America. 



