The Virgin Is., with St. Croix, Anguilla, and the St. Bartholomew group (all of which are non-volcanic islands), are related to Porto Rico, while Guadeloupe and all the islands to the south, up to Grenada (all of which are volcanic), show marked traces of S. American influence. St. Kitt’s, Antigua, and Montserrat may be regarded as intermediate between the two groups. St. Thomas, St. John, and Tortola have each one _Plagioptycha_ and one _Thelidomus_, while St. Croix has two sub-fossil _Caracolus_ which are now living in Porto Rico, together with one _Plagioptycha_ and one _Thelidomus_ (sub-fossil). The gradual disappearance of some of the characteristic greater Antillean forms, and the appearance of S. American forms in the Lesser Antilles, is shown by the following table:-- +-----------------------+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | | | | | | | | | | | | | | | S | | | | | P | S | | | | | S | | G | | M | | | t | | | | | o | t | | S | | | t | | u | | a | S | | . | | | | | r | . | | t | | A | . | | a | D | r | t | B | | | T | | | t | | S | . | T | n | | A | d | o | t | . | a | V | G | r | | | o | T | t | | o | g | K | n | e | m | i | | r | i | r | i | | | | h | . | C | r | u | i | t | l | i | n | L | b | n | e | n | | | R | o | | r | t | i | t | i | o | n | i | u | a | c | n | i | | | i | m | J | o | o | l | t | g | u | i | q | c | d | e | a | d | | | c | a | a | i | l | l | ’ | u | p | c | u | i | o | n | d | a | | | o | s | n | x | a | a | s | a | e | a | e | a | s | t | a | d | | | . | . | . | . | . | . | . | . | . | . | . | . | . | . | . | . | +-----------------------+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | Bulimulus | 7 | 4 | 2 | 4 | 1 | 2 | 2 | 3 | 8 | 9 | 5 | 3 | 3 | 6 | 2 | 4 | | Cylindrella | 3 | 2 | 1 | 1 | 1 | . | . | . | 1 | . | 1 | 1 | 1 | . | . | 1 | | Macroceramus | 3 | 1 | 1 | . | 2 | 1 | . | . | . | . | . | . | . | . | . | | | Cyclostomatidae, etc. |23 | 4 | 1 | 5 | 1 | 1 | 1 | . | 4 | . | . | . | . | . | . | 1 | | Dentellaria | . | . | . | . | . | . | 1 | 1 | 8 | 5 |11 | 2 | 2 | . | 1 | 1 | | Cyclophorus | . | . | . | . | . | . | . | . | 1 | 2 | 2 | . | . | . | . | . | | Amphibulimus | . | . | . | . | . | . | . | . | 2 | 3 | 1 | . | . | . | . | . | | Homalonyx | . | . | . | . | . | . | . | . | 1 | 1 | . | . | . | . | . | . | +---------------------------------------------------------------------------------------+