by r. m. johnston, f.l.s, 85 



Univalves — 



21. Dulvertonensis, Ten. Woods. 



22. Huonensis, Ten. Woods. 



23. unicarinata, Ten. Woods. 



24. Dunrobiueusis, Ten. Woods. 



25. Tasmauica, Ten. Woods. 



26. Pomatiopsis striatula, Aienke. 



27. .^^.ssiminea Tasmanica, Ten. Woods. 



28. Planorbis Tasmanicus, Ten. Woods. 



29. Paludestrina Legraudiana, Brazier. 



30. Wisemaniana, Brazier. 



31. Unio Moretouicus, Sowcrby. 



32. Pisidium Tasmauicum, Ten. Woods. 

 38. Dulvertonensis, 7'en. Woods. 

 34 Cyclas Tasmanica, Ten. Woods. 



In this first paper of Mr. Woods', he was only able to deal 

 with the sheM. or exo-skeletou in this scheme of classification. 

 That this was due to lack of materials at the time, however, 

 rather than choice, is amply proved by his elaborate memoir 

 *' On some Tasmanian Patellidae," contributed in the following 

 year (May, 1876), where he minutely describes in an ad- 

 mirable manner the various species examined by him (eight) ; 

 the malcological characters of each animal, including the 

 odontophore, lingual plate, or radula, having received the 

 greatest attention. 



The appearance of Mr. Woods' paper, therefore, was hailed 

 with much satisfaction by local naturalists, and it speedily 

 had the effect of drawing the attention of other observers to 

 this neglected branch of study. Among these, the writer 

 was the first to follow up the work begun by Mx*. Woods, and 

 the results of mauy observations were communicated to this 

 Society in the year 1877, in a paper entitled " Further Notes 

 on the Fresh Water Shells of Tasmania." 



My numerous explorations in nearly all parts of the island 

 afforded me rare opportunities for collecting and for observing 

 the varying chai'acter of the same species in different habi- 

 tats. The extreme variability of the prevailing forms par- 

 ticularly arrested my attention, and a lengthened examination 

 of some of them enabled me to draw particular attention to 

 the unstable character of some of the distinctions which Mr. 

 Woods deemed at first to be of specific value. Among these 

 I specially drew attention to the influence of local environ- 

 ment, such as altitude, volume, and degree of brackishuoss 

 of water, in modifying size, transparency, and colour ; and iu 

 the genera Physa Lymnoea and Bithyuella, I pointed out the 

 <langer of depending upon the presence or absence of con- 

 tinuous or discontinuous cilia), spiniform cilito or ciliated 

 membranous keel, as characters of specific value. 



