240 Transactions. — Zoology. 



Diplodon lessoni, Kiister (1856). 



Unio lessoni, Kiister, Conch. Cat., 1856, p. 135, pi. xxxvi., fig. 4. 

 Type from New South Wales. 



Lake Wakatipu (Stat. 37— Dredged in 10 ft. to 30 ft.).— 



Nine specimens were 

 obtained. Shell (fig. 4) 

 oblong, obliquely trun- 

 cated behind, com- 

 pressed, inequilateral, 

 beaks strongly eroded 

 in all specimens, no 

 trace of sculpture left ; 

 surface with distant 

 flatly elevated rest- 

 marks, which, together 

 's * with the intervening 



space, are covered with 

 very fine thread-like concentric fines ; towards the base and pos- 

 terior margin the growth-lines are more distinct and slightly 

 foliated. There is no trace of radial sculpture. The epidermis 

 is olive to dark-brown, dull. Interior bluish nacre, with yel- 

 lowish patches under the beaks, where there are several deep 

 small dorsal scars. Right valve : The pseudocardinals are com- 

 pressed, the anterior upper tooth is small, grooved, the posterior 

 tooth much larger and crenate ; the lateral tooth is slightly 

 arched and rugose posteriorly. Left valve : Anterior pseudo- 

 cardinal compressed, tongue-shaped, slightly rugose, the pos- 

 terior subtriangular, deeply denticulate ; the laterals are of 

 nearly equal height and crenate posteriorly. 



The largest specimen was selected for the diagram and de- 

 scription, and its dimensions are — Length, 51 mm. ; height, 

 30 mm. : diam., II?, mm. 



I submitted specimens to Dr. W. H. Dall, Hon. Curator of 

 Mollusks, U.S. Nat. Museum, for examination, and he very kindly 

 informed me that according to the material in the museum they 

 are D. lessoni, Kiister. 1 have not seen any Australian speci- 

 mens, nor the description and figure published by Kiister, but I 

 do not hesitate to accept Dr. Dall's view, although some may 

 think it hazardous to refer our shell to a New South Wales species. 

 I have not seen this species from anywhere else in New Zealand. 

 Dr. Vim Jhering once suggested that a number of measure - 

 ments should be taken to ascertain the range of variability in 

 qiecies of the family UnionidoB. I have measured a great num- 

 ber of specimens from New Zealand some years ago, and may 

 publish the results later on. I have done the same for a number 

 of the Unionidrr collected by .Messrs. Lucas and Hodgkin, and 



