Diploion.\ I'ELECYPODA. 941 



more straight than in typical D. Menziesi. The beaks are much 

 corroded in all the specimens I have seen. The shell is rather 

 thin, yellowish-brown, with strong concentric sculpture, approaching 

 D. rugatxs, Hutton. The interior is nacreous olive, the hinge not 

 different from that of the type. 



Length, 70 mm. ; height, 40 mm. ; diameter, 16 rnm. 



Type in my collection. 



Hub. Lake Omapere (Miss Willis). 



'Subsp. aucklandicus, Gray, 1843. Plate 59, fig. 4. 



Unio aucklandicus, Gray, Dieff. N.Z., 1843, 257 ; Conch. Icon., xvi, pi. 29. 

 f. 156 ; M.N.Z.M., 161 ; Medley and Suter, P.L.S. N.S.W. (2), vii, 662. 

 U. Menziesi aucklandica, Gray : Suter, J. tie Conch., xli, 290 ; T.N.Z.I., 

 xxxvii, 234. 



Distinguished from the species by the subparallel dorsal and basal 

 margins, the greater thickness of the shell, and the posterior dorsai 

 margin being but faintly winged ; the anterior end is regularly convex, 

 the posterior end not very much higher than the anterior, obscurely 

 convexly angled. Nodulous radiate sculpture is nearly always present. 

 In the right valve the posterior pseudo-cardinal is stout, triangular, 

 the anterior minute ; in the left valve the 2 pseudo-cardinals are both 

 strong and corrugated. 



Length, 58 mm. ; height, 31 mm. ; diameter, 17 mm. 



Type in the British Museum. 



Hab. Bay of Islands, type (Dr. Sinclair) ; creeks in the vicinity 

 of Auckland ; Henderson Creek ; Wairangi, Waikato ; Pukekohe : 

 Lake Taupo ; Lake Waikaremoana ; Virginia Lake, Wanganui ; Wai- 

 mate ; Lake Coleridge. 



Remarks. In 1905 I followed Simpson in uniting this form with 

 the species, as almost all intermediate grades may be found. How- 

 ever, this can also be said to be the case with most of the other sub- 

 species, and I think it is more in the interests of science to separate 

 a number of more or less distinct forms which are produced by 

 differences in their environments. Too much lumping does not tend 

 to advance scientific knowledge. D. aucklandicus, as described by 

 Gray and figured by Reeve, can always be separated from D. Menziesi, 

 and intermediate forms may be assigned to one or the other, or 

 denoted as intermediate between the two. 



Fossil in the lignite -beds of Dunstan, Otago, probably older 

 Pliocene. 



Subsp. depauperatus, Hutton, 1883. Plate 59, fig. 5. 



Unio dcpauperc-tus, Hutton, N.Z.J.S., i, 1883, 478 ; T.N.Z I., xvi, 1883 

 (1884), 210 ; Hedlcy and Suter, P.L.S. N.S.W. (2), vii, 663. U. mulabilis, 

 Lea : Suter, J. de Conch., xli, 291 ; not of Lea. Diplodon Menziesi 

 depauperatus, Hutt. : Simpson, Proc. U.S. Nat. Mus., xxii, 1900, 890 : 

 Index, 91. 



Shell very thin, oblong, compressed ; beaks small, mostly eroded. 

 Anterior end short, rounded ; posterior end slightly winged, obliquely 



