Webster. — Additions to the New Zealand Faima. 311 



Hab. Waipipi, on mud-flat. 



The operculum and sculpture of shell are similar to Siphon- 

 alia ; the dentition is nearer Trophon. 



Phrixgnathus serratocostata, n. sp. Figs. <±, ia. 



Shell of four and a half rounded whorls, horny without 

 markings ; the limitation of the coarse protoconch is not clearly 

 defined, but there is a one-and-a-half-whorled smooth apex ; 

 the body- whorl has twenty- one flanges, wide on the periphery 

 and rapidly diminishing towards the suture, the entire length 

 beset with close-set hooked teeth, turned towards the apex : the 

 spaces between are clearly reticulated with revolving and in- 

 cremental striae ; the flanges are not continued on the base, 

 but are represented by stria? of varying strength. Periphery 

 bluntly angled; columella widely reflexed above, perforation 

 about one-twelfth of the major diameter. Major diameter, 

 1 mm. ; height, 075 mm. 



Hab. Waiuku. 



Two specimens, one with the animal ; but as my microscope 

 does not easily separate very minute teeth I have deferred 

 mounting the radula, and depended only upon shell charac- 

 teristics. 



Unio (Diplodon) websteri, Simpson. Figs. 5, 5a, 56. 



As this shell has not yet been figured, I give a careful pen- 

 and-ink drawing, after accurate measurements both of outline 

 and sculpture. I also at fig. 6 give a similar drawing of Di- 

 plodon nova?-hollandio?, Gray, for comparison. 



Mr. H. Suter* says, " I consider Diplodon websteri as a D. 

 menziesi in which the nodulous sculpture is developed to the 

 highest degree." If this is correct we should find every stage 

 of nodulous development ; such is, however, not the case as far 

 as I am aware. There is, I believe, nothing between the mere 

 indications of such sculpture in D. menziesi and the fully de- 

 veloped D. websteri. I have recently seen a single valve of this 

 shell in Mr. R. Murdoch's collection : it was found in the Wanga- 

 nui River. The hinge of Simpson's species (which must not 

 be confounded with Unio websteri, Wright) is much more de- 

 veloped than that of D. menziesi. The shell I have figured 

 is the co-type, the type being in the Smithsonian Institute 

 at Washington. I have other specimens in which the nodules 

 are carried out to the anterior margin, and the outline approxi- 

 mates more to that of the Australian shell, inasmuch as the 



* Trans. N.Z. Inst,, vol. xxxvii, ]>. 236. 



