167 



parison of these two lists the progress of our knowledge of 

 systematics will clearly be shown. 



Fam. Lepidopleuritlae. 



Lepidopleurus (35), Cosmopolitan. 



Hanleya (4), North Atlantic to Florida, South Africa. 

 Hemiarthrum (1), South Georgia, Kergueleu. 

 Choriplax (= Microplax) (1), Australia. 



Fam. Ischnocliitonidae. 



Tonkella (5), Holland '), Ireland, North Atlantic, North Pacific 

 to Japan, California, Aleutian Islands. 



Schizoplax (1), Aleutian Islands. 



Callochiton (10), and Trachyradsia — including Ischnochiton stearnsi 

 Dall — (5), England, Mediterrauean, Ceylon, Australia, Indo- 

 Malayan Archipelago, Straits of Magellan, Farallones Islands. 



Trachyderm on . 



Trachydermon s. str. (14), Atlantic and North European Seas, 

 Mediterrauean and Adriatic Seas, North Pacific, Arctic, 

 Philippines, Chili, Peru, Porto-rico. 

 Boreochiton (3), Northern Seas of Europe, Arctic, North 



Pacific, ïierra del Fuego, South Georgia. 

 Spongioradsia (3), North Pacific, Japan. 

 Cyanoplax (3), Westcoast of North and South America. 



Chaetopleura (25), Westcoast of South America to Cape Horn, 

 California, Patagonia, Central America, Eastcoast of Arae- 

 rica from Masachusetts to Florida, West India, Brazil, 

 Portugal, Cape of Good Hope, Natal, East Asia, Australia. 



Pallochiton (2), California. 



Dinoplax (2), South Africa. 



Variolepis (1), Chili. 



1) I never saw specimens of Tonicella from the coast of Holland. The only Chitons, 

 found by me on the Dutch coasts, are Trachydermon cinereus L. and Lepidopleurus 

 cancellatus Sow. 



