72 AUSTRALIAN HIRUDINEA, VI., 



The Uerpohdellidce include: — ■ 



Cylicobdella Grube, 1871; South America and West Indies. 



Lumbricobdella "Kennel, 1886; South America aud West Indies. 



Orohdella Oka, 1895; mountains of Japan. 



Forbes, in 1890, also recorded the occurrence of a terrestrial 

 species, in North America, of the genus Semiscolex, whose 

 members are generally aquatic. 



In comparing now the distribution of these forms with that of 

 aquatic forms, it will be seen that the former are much more 

 limited and do not enjoy a cosmopolitan distribution. 



The Hirudinea in general were probably derived from an 

 aquatic ancestor; and, in view of the fact that the great majority 

 of species are still aquatic in habit, we must regard the terres- 

 trial forms as being specially modified for a terrestrial existence, 

 or as having specially adapted themselves to an environment 

 quite different from that under which the majority of the forms 

 have maintained their existence. 



It might be merely suggested that the adaptation of some 

 forms to a terrestrial existence might be due to the adaptation 

 of an aquatic host by evolution to terrestrial conditions. This 

 suggestion would receive some weight from the argument, which 

 is well supported, that the Hirudinea represent an archaic 

 group. At the same time it is to be borne in mind that several 

 of the terrestrial Gnathobdellidce differ in only a small degree 

 from certain allied aquatic forms of the same group. 



In New Zealand, no land-leeches have yet been noted. Mr. 

 Moore, of the United States National Museum, and Prof. 

 Benham have shown definitely that the s^iecimens of Geobdella 

 limbata ascribed to New Zealand are identical witli H. {Chthonob- 

 della) limbata described by Grube from Sydney, and no doubt 

 this represents the locality whence they were obtained. Further, 

 land-leeches would certainly have been discovered long ago if 

 they existed in the New Zealand bush. Two terrestrial genera 

 have been noted in Australia, viz., Philoimon and Geobdella. 

 Both these forms are very characteristic, and exhibit points of 

 special interest. Philcemon fungens is the sole species known of 



