36 JOURNAL OF CONCHOLOGY, VOL. II, NO. 2, APRIL, I904. 



(5) Faunula limphana, comprising certain springs in the Sor- 

 rentine Peninsula and Capri: 



Ancylus flimiatilis Pseudamnicola macrostoma 



LimncBa triiiicatula 



All the freshwater shells of Naples originated in the tertiary period 

 and have undergone progressive development from the inferior 

 pliocene to present times; more than a third were already differentiated 

 in the pleistocene, but the varieties are all more recent. The follow- 

 ing genera originated in the Jurassic period: — Planorbis (in the lias 

 vide Sandberger), Fhysa, LivmcRa, Neritina (one of the oldest; N. 

 Hasina Dunker, occurs in the Schlotheimia angulata beds of AViirttem- 

 berg, and the species became more abundant in the upper eocene), 

 Pseuda7imicola, Valvata, Unio. Of cretaceous origin are Bithynia 

 {B. prcRcursor Sandb., is the earliest from the cretaceous rocks of 

 Hanover), Sphceriiwi (English wealden). The following are tertiary: — 

 Ancyhis (eocene), Pisiditim (inferior eocene of Paris), Atiodonta 

 (inferior miocene of Germany). 



Of the species the least abundant are those of pliocene origin. This 

 fact agrees with all geological principles, because few species have 

 been able to endure the climatic changes that took place in this and 

 later periods. Our fauna belongs to the same type as that of Central 

 Europe, which took its rise in the Alpine regions; the species that 

 constituted that primitive fauna gave rise to others which have varied 

 more or less according to their distance from the centre of dispersion. 

 The geographical distribution of the Neapolitan freshwater shells is 

 very extensive because the dispersal of these organisms is in direct 

 relation to their size. Our fluviatile mollusca have originated in the 

 zone called Bourguignat^ "de creation," or better, by Locard- "d'ap- 

 parition." This zone lies between 25° and 36° N. lat., and coincides 

 with a series of mountain chains stretching from the Adantic to the 

 Caspian. We may seek the origin of our species in the Alpine centre, 

 one of three parts into which the zone is divided. 



GASTROPODA. 

 PULMONATA. 



LlMN.EID^. 



(i) Ancylus (Ancylastrum) fluviatilis Miiller. — "Verm. Hist.," 

 II., p. 201, nr. 386, 1774; Drap., "Tabl. Moll.," 1801, p. 47 ; Phil, 

 "Moll. Sic," I., 1836, p. 120; II., 1844, p. 93. In colonies in clear 

 and running waters on stones (Sebeto, Monte S. Angelo, Castellam- 

 mare, Sorrento and Meta). 



1 "Malacologie de I'Algerie," 1864, vol. 2, p. 366. 



2 "'Etudes sur les variations malacologiques de la faune du bassin du Rhone," II., p. 241. 



