MORPHOLOGY OF THE HELICINIDJ!. 761 



Seychelles, and Pseudotrochatella undulata Morelet is a subfossil 

 form from Mauritius. Xone is known from Madagascar. 



In a recent work of great value to the student of geographical 

 distribution A. J. Wagner (12) has revised the family Helicinidae, 

 and, founding his diagnoses chiefly on the characters of the 

 operculum, has broken up the old genus Uelicina into no less 

 than thirteen genera, reserving Lamarck's appellation for the 

 American and Antillean forms which conform to the oiiginal 

 definition of the geniis. Of the remainder I mention the largest 

 genera. Sidfurina has its centre in the Philippines and extends 

 thence to the Andamans, Nicobars, IMoluccas, New Guinea, and 

 Tahiti. Ajj/tanoconia, which also seems to be centred in the 

 Philippines, extends wideh', to Japan. S. China, the Malay 

 Archipelago, the Andamans, Nicobais, Seychelles, Moluccas, and 

 through Micronesia and Melanesia to the Paumotu and Sandwich 

 Islands. Shiranya has its centre in Fiji and Tonga, and extends 

 thence to the Carolines, Sandwich, Society, Hervey, and Solomon 

 Islands. Orohojihana is found in Queensland and N.S. Wales and 

 extends through nearly the whole of Polynesia. Pcdceohelicina, 

 with its subgenus Ceratopoma, is again a Philippine genus, and 

 extends to New Guinea, the Bismarck Archipelago, the Solomon, 

 Louisiade and Pelew Islands. The last-named genus is, according 

 to Wagner, closely allied to Uelicina sensu restricto. Again, the 

 subgenus Retorquata of Uelicina, which occurs in Mexico and 

 Centi'al America with outliers in Florida, and Texas, aftbrds, 

 according to the same author, a transition to such a characteristic 

 Antillean genus as Alcadia. A consideration of these statements 

 leads to the conclusion that the Helicinida? are capable, by what 

 means we know not, of wide dispersal across seas and oceans, and 

 find conditions most suitable to their existence in proximitv to 

 the sea. They appear to have originated in RLexico and Central 

 America, and to have spread eastwards to the Antilles, whei'e 

 they found the conditions specially suitable, and have been 

 differentiated into several genera (Alcadia, Lucidella, Entrochatella, 

 PriotrochateUa, Froserpina) and numerous species, and one species 

 [H. substriata convexa Pf.) has found its May to the Bermudas. 

 Others have extended down the eastern coast of S. America, but 

 the Atlantic Ocean has proved an impassable barrier to their 

 further extension eastward. On the Pacific side the grou}) has 

 been transported by some means unknown to us to the Pacific 

 Islands, and it would appear from the evidence that it did not at 

 first effect a lodgment in the moi-e eastern islands, but in the 

 Pliilippines, from which centre it has spread in all directions — 

 eastward throughout Polynesia and to the Sandwich Islands, 

 southward to New Guinea and Australia, northward to Japan 

 and China, westward through the Dutch Indies and Malaya to 

 the Andaman and Nicobar Islands. Very few have ti^versed 

 the Indian Ocean to reach the Seychelles and Mauritius. 



Very little is known of the geological history of the group. 

 Uelicina occurs in the post-Pliocene of N. America, but the 



