34 JOURNAL OF CONCHOLOGY, VOL. II, NO. 2, APRIL, I9O4. 



The present paper is the result of some years, of enquiry. I have 

 had the good fortune to be able to inspect Costa's collection, and also 

 various specimens determined by Philippi himself, as well as my own 

 collection, whilst those of Cavaliere Praus and of my friend the late 

 Baron Castriota-Scanderbeg, rich in forms determined by Philippi, 

 Tiberi, Blanc and Monterosato, have provided me with valuable 

 materials for study. 



The greater number of species and individuals are found in the 

 volcanic regions of Vesuvius and the Phlegrsean fields, which extend 

 to the edge of the Sorrentine calcareous ridge, and are rich both in 

 streams and stagnant waters. The Sorrentine peninsula, which boasts 

 little level land and consequently little water, is poor in freshwater 

 specimens, but owing to the composition of the earth, abounds in 

 land shells.^ 



Naples and the surrounding district are watered by the Sebeto and 

 Sarno rivers. The first, known also as the Rio della Maddalena, 

 rises in BoUa, near Vesuvius, and crosses the marshes north-west of 

 Nola, where it divides into rivulets and irrigation channels, and finds 

 its outlet in the Bay of Naples, near the Ponte della Maddalena. 

 This little river separates the Vesuvian or basaltic from the Phlegr^an 

 or trachytic region. The Sarno is formed by the union of three 

 streams at the east of San Severino (Salerno), flows from east to west, 

 and discharges into the Gulf of Naples north of Castellamare and 

 south of Torre Annunziata. 



Stagnant waters where freshwater shells may be collected are the 

 Lago di Patria, at the end of the Phlegrgean fields, the little lake of 

 Astroni, at the bottom of the crater of the same name, the fountains 

 of the royal park of Capodimonte, of the Villa Nazionale and Botanical 

 Garden in Naples, and a few places in the Sorrentine peninsula and 

 in Capri. 



In all twenty-five species of freshwater shells, with numerous 

 varieties, are found in this region; in the calcareous district there are 

 only three species. 



In enumerating these species I have adopted a mean between two 

 extreme positions : that which differentiates every recognisable variety 

 as a species, and the other which groups the forms under certain 

 designations. A species is not an invariable quantity, and conse- 

 quently, in the sense used by Linnseus and Lamarck, no longer exists, 

 but there are many types with decisive characters, and not very clearly 

 related to surrounding forms. It is questionable whether we ought to 



I R. Bellini, " MoUuschi extramarini dell'isola di Capri," Boll. Soc. Zool. Ital. vol. i, 

 1900 ; " Alcune osserva^ioni sulla distribuz. ipsometrica dei molluschi terrestri nell'isola di 

 Capri," Rcndiconto del Convegno in Napoli dell Unione Zoolog. Italiana, 10-13 Aprile, 1901. 



