506 Transactions. 



The next most numerous shell is a large form of Quintalia stoddarti, 

 intermediate between Q. s. stoddarti (Gray) from Phillip Island and Q. s. 

 floscuTa (Cox) from the main island. 



A rarer shell is a fine large variety of Advena campbellii called Ad vena 

 campbelli nepeansis. It is much larger and more flattened that either the 

 Phillip Island or main-island forms. 



Succinea is well represented, and at the present time it is impossible to 

 decide the truth regarding these. Two species are separated, a very large 

 slender elongate form called Succinea nepeanensis, and a more common one 

 with shouldered whorls named Succinea humerosa. This might be best 

 considered as the representative subspecies of the mainland S. norfolkensis 

 Svkes, than which it averages larger in size. 



Omphalotropis is also fairly well represented, but the variation in 

 sculpture and form known in this genus has prohibited the differentiation 

 of the Nepean Island subfossils. 



One of the most interesting items to me was the discovery of Fanulum 

 insculptum (Pfeitt'er), occurring rarely; whilst one specimen of Fanulum 

 imitatrix (Sykes) was observed. Altogether a number of the F. insculptum 

 (Pfeiffer) were separated, and, though they have not been named, they 

 average smaller and more conical than the living main-island form. 



The reason for the extinction of these Nepean Island molluscs is at 

 present unknown, but the facts seem to show that the species formerly 

 living were of larger size than the present existing species, whilst the 

 Fanulum seems to show the reverse — that is. the examination of the 

 available material, which is not small, tends to the conclusion that whereas 

 Advena, Quintalia, and Mathewsoconcha (probably also Succinea) have 

 decreased in size or become extinct, Fanulum has increased in size and 

 numbers, but whether at the expense of the other genera is not evident. 



Mr. Roy Bell was unable to collect on Phillip Island, but four species 

 have been described from that locality viz., Belloconcha phillipii (Grav), 

 Belloconcha grayi (Sykes), Advena campbellii (Gray), and Quintalia stoddarti 

 (Gray). The latter two are still represented on both Nepean Island and 

 the main island, but the exact relationships of these are not known. The 

 type set of Quintalia stoddarti (Gray) are much larger than the very long 

 series from Nepean Island, which again greatly exceed in size the living 

 main-island shells, which also differ in their more conical form. These 

 three are ranked as subspecies only, and there seems little doubt as to the 

 accuracy of this determination. The type, however, of Advena campbellii 

 (Gray) is a small shell not much larger than the living main-island form. 

 As the subfossil Nepean Island shells are much larger and more depressed, 

 the suggestion at once occurs that the type from Phillip Island may not 

 be representative of the form there living. 



The species Belloconcha phillipii (Gray) is the giant of the genus, whilst 

 Belloconcha grayi (Sykes) is also a large species. These both surpass the 

 subfossil Nepean Island species, whilst on the main island only one small 

 species has been found alive, and so far with very restricted habitat, though 

 two other small species have been found subfossil. 



I hope later to be able to record the results of a new search for Phillip 

 Island molluscs, and note their relationships. 



It remains to note that four species recorded by Sykes were not 

 obtained by Roy Bell — viz., Charopa exagitans (Cox), C. ? depsta (Cox), 

 C. ? quintali (Cox), and 0. ? patescens (Cox). From the published de- 



