185 



The Gastropods of the Older Tertiary of 

 Australia. (Part III.)* 



By Professor Ralph Tate, F.G.S., F.L.S. 



[Read October 7, 1890.] 



FAMILY TRICHOTROPID.^. 



The ten species of this family forming part of the Eocene 

 fauna of Australia are all congeneric ; but I am uncertain as to 

 their correct location — whether with the type genus or with 

 Mesostoma. 



Mesostoma was defined by Deshayes in 1864, and included in 

 it four species from the Parisian Eocene ; the genus was referred 

 to the Family Rissoidee. In my Appendix to Woodward's 

 Manual of the Mollusca, 1867, I ventured to transfer it to the 

 Family Cerithiidse, in which arrangement I am followed by Tryon 

 in his Systematic Conchology, 1883. In my "Census of the 

 Fauna of the Older Tertiary of Australia," Roy. Soc, N.S. 

 Wales, October 3, 1888, I referred our species to '■^Mesostoma (if 

 distinct from Tinchotrojns ),'' and was disposed to regard Tricho- 

 trojns inornata, Hutton, recent and fossil in New Zealand, as 

 congeneric therewith. Dall, in his Report of the " Blake " Mol- 

 lusca, Part II., June, 1889, places Mesostoma as a subgenus 

 under Tricliotroiyis, without, however, indicating the differential 

 characters ; but remarks that " the degree of affinity which 

 Mesostoma^ Dolophanes, (tc, bear to the original type of the 

 family yet remains to be determined." 



So far as my own investigations permit me to form an opinion, 

 I fail to appreciate any differences of generic value, from a con- 

 chological point of view, between Triclwtropis and Mesostoma. 



* In the natural sequence of the families, Margin ellidfe, Columbellidse, 

 and Pleiirotomidas should have formed part of this or the preceding fasci- 

 culus ; but because of the difficulty experienced in correctly illustrating 

 the species of the first two families, which are for the most part small or 

 minute, their inclusion has for the present been abandoned. In respect of 

 the Family Pleurotomid^e, the cause of their temporary exclusion is want 

 of leisure to elaborate the very numerous species (not less than 60) of this 

 perplexing group. 



Eleven species of Marginella have been described, though not figured ; 

 of Columbeila, represented by about 26 species, very few are diagnostically 

 known ; but of Pleurotomidge about 20 have been described, and about 

 half of them figured. 



The plates to illustrate this communication are unavoidably postponed. 



