1897.] NATURAL SCIENCES OF PHILADELPHIA. 361 



the text on p. 94, there are three denticles on this tooth, but the 

 description on p. 96 gives five denticles. The outer uncinus has 

 seven denticles. The denticle formula of what Martens and PfefFer 



identify as Eatoniella kerguelenensis is, therefore, _ 7 , 5, 3 (?), 7. 



1-1 (?) 

 In Dardania Hutton, 2 which, so far as shell, operculum and rad- 

 ula go, is identical with Eatoniella, the dentition as figured by Hut- 

 ton agrees in essentials with that genus. Hutton's figure is rather 



diagrammatic. It shows no basal denticles, the formula being 5 t 



0-0 

 6, 3, 5 (?). This seems to agree essentially with Eatoniella, espe- 

 cially in the important and unusual character of the inner marginal 

 tooth, the cusp of which is remarkable for the small number and 

 large size of its denticles. The omission of basal denticles may be 

 an oversight. 



The inclusion of Dardania in Eatoniella seems from the data at 

 hand to be necessary. 



Now, in Tatea, the radula (PI. IX, fig. 8) is unequivocally Hy- 

 drobioid. Judging from it alone, if one were to ignore the shell 

 and operculum, it would be pronounced a Potamojiyrgus. It differs 

 in very important particulars from that of Eatoniella. The rachi- 

 dian tooth shows several well marked basal denticles inserted well 

 above the basal margin of the tooth, as in the freshwater genera. 

 The lateral is as usual above, and has the tongue-like process be- 

 low, noticed in many non-marine forms. The inner uncinus has 

 the scythe-like form usual in Hydrobia and its allies, with 15 to 20 

 minute denticles on the long cusp. The outer uncinus has still 

 finer denticulation. It will be seen that both the median and the 

 inner marginal teeth are quite different from the corresponding teeth 

 of Eatoniella, and altogether like those of Potamopyrgus and its allies. 



From these characters we would advocate the removal of Tatea 

 from the subfamily Rissoinino3, and install it in the Amnicolidm 

 (Hydrobiidce of Fischer), notwithstanding its aberrant operculum. 

 The union of Tatea with Eatoniella, which some authors have ac- 

 cepted, is altogether inadmissable ; and the genus, which is dedi- 

 cated to one of the most able of Australian zoologists, will stand as 

 one of the most isolated in its family. 



The figure represents the teeth of T. huonensis ; those of T. para- 

 disiaca are very similar. I have not examined the radula of T. 

 rufilabris. 



2 Trans, and Proc. N. Z. Institute, xiv, p. 147, pi. 1, f. K, 1-4, (1882) 



