532 PATAGONIAN EXPEDITIONS I ZOOLOGY. 



The growth of the shell in Patagonian species is periodic, growth-arrest 

 periods being marked by streaks interrupting the normal pattern. On 

 resumption of growth, the zigzag pattern is sometimes replaced by irregu- 

 lar streaks ; but in a later growth-period the original pattern may be 



resumed. 



The subgenus Pseudochilina was based upon a form shaped about like 

 fig. 7 of Plate XLIII. The irregular or fibrous surface, which served to 

 characterize the subgenus, seems to me to be wholly due to erosion, the 

 cuticle or periostracum being lost from the unique type in the National 

 Museum. In other characters the shell is a typical Chilina. 



Acyrogonia of Mabille and Rochebrune is a Chilina in which the colu- 

 mellar plait is wanting. I have found this plait variable in development 

 in some forms of Chilina from the Rio Chico. In C. fulgurata oligoptyx 

 it approaches the condition described in Acyrogonia. 



DISTRIBUTION OF CHILINA. 



Chilina occupies the temperate and cold zones of South America from 

 the Tropic of Capricorn to Cape Horn. No member of the group, either 

 living or fossil, has been found outside of these limits. 1 It is noteworthy 

 that no trace of the group has been found in other Austral lands --Tas- 

 mania and New Zealand having sufficiently similar climatic conditions to 

 favor the survival of Chilinidce, if the family ever had a wider range in 

 the Antarctic area. 



Within their area, the Chilinidcz are abundant snails in all suitable sta- 

 tions, as Physidce are in the north. They swarm in springs, small streams, 

 lakes, and in some places the margins of rivers. They are most abundant 

 southward, becoming rarer and local toward the northern borders of their 

 range. 



The species from west of the Andes are in all cases, so far as we know, 

 distinct from those east of the divide. In the cold temperate and cold 

 zones at least, the widely diverse physical features on opposite sides of 

 the Andes would lead us to expect different snail faunas. 



^Chilina olivida Repelin, Ann. Mus. d'Hist. Nat. de Marseille, VII, p. 69, of the Cenomanian 

 of central France, has no columellar fold, and is clearly a Lymnseid snail with no relations what- 

 ever to Chilina. Chilina in Europe, like Partitla, Polygyra, Glandina, etc., is one of those myths 

 of European palaeontology which astonish and amuse the investigator using modern methods with 

 Pulmonate snails. 



