CHAP, xiv.] THE NEOTROPICAL REGION. 75 



islands. Of Cerambycidse there are 16 genera, 2 of which range 

 all over America, 4 are Neotropical, 1 South American only, 

 while the following are confined to the islands, Merostenus, 

 Pentomacrus, and Eburiola (Jamaica) ; Bromiades (Cuba) ; 

 Trichrous, Heterops, and Pceciloderma (Antilles). One genus, 

 Smodicum, is widely spread, having a species in Carolina, 1 in 

 South America, 1 in Hayti, and 1 in West Africa. Of Lamiidse 

 there are 14 genera, 8 of which are Neotropical, 1 common to 

 Central America and Mexico, 1 to the United States and Cuba, 

 while 2, Proecha and Phidola, are confined to Cuba. Several of 

 the genera are curiously distributed \-Spalacopsis is South 

 American, with 4 species in Cuba and Tropical Africa ; Lago- 

 cheirus is Neotropical, with a species in Australia ; while Lepto- 

 st^lus is characteristic of the Antilles and North America, with 

 a few species in South America, and one in New Zealand. 

 These cases of erratic distribution, so opposed to the general 

 series of phenomena among which they occur, must be held to 

 be sufficiently explained by the great antiquity of these groups 

 and their former wide distribution. They may be supposed to 

 be the remnants of types, now dying out, which were once, like 

 Callichroma, Clytus, and many others, almost universally dis- 

 tributed. 



All the peculiar Antillean genera of Cerambycidse and La- 

 miidae are allied to Neotropical forms. The peculiar Prionidae, 

 however, are mostly allied to Mexican and North American 

 groups, and one, Monodesmus, belongs to a group all the other 

 genera of which inhabit the East Indies and South Africa. 



Land-shells. This subject has already been generally treated 

 under the Region, of which, in this class of animals, the Antilles 

 form so important a part. We must therefore now confine our- 

 selves mainly to the internal distribution of the genera, and to 

 a few remarks on the general bearing of the facts. 



The excessive and altogether unexampled productiveness of 

 the West Indian islands in land-shells, may be traced to two 

 main sets of causes. The first and least known, consist of the 

 peculiar influences and conditions which render islands always 

 more productive than continents. Whatever these conditions 



