238 Transactions. — Zoology. 



(2.) Lake Rotoiti (Stat. 8— Obtained by dredging in 12 ft.).— 

 Two specimens of medium size, strongly concentrically ridged, 



uml es much eroded, posterior end subtruncated, not yet 



distinctly biangular. They represent the intermediate stage 

 between the young menziesi and the full-grown hochstetteri. 

 Interior olive-bluish, pearly, a row of .small dorsal scars in the 

 umbonal cavity, parallel to the hinge line. Muscular scars 

 strongly impressed. Right valve with two very unequal pseudo- 

 cardinals, the anterior small, lamellar, the posterior compressed, 

 with a broad posterior base, crenulated, trifid ; the lateral tooth 

 slightly curved, narrow, high, truncate and corrugate posteriorly. 

 Left valve with the two pseudocardinals coalescent, separated 

 only by a groove, the anterior strong, triangular, rugose. The 

 two laterals with crenate edges, obliquely truncated behind. 

 The dimensions of the two specimens are — Length, 50 mm. ; 

 height, 3-1 mm. ; diam., 16 mm. : and, length, 41 mm. ; height, 

 29 mm. ; diam.. 12-5 mm. 



Diplodon menziesi, Gray, subsp. rugata, Hutton (1883). 



TJnio rugatus, Hutton, N.Z. Journ. Sci., vol. i., 1883, p. 478. 



Laic Waikare (Stat. 41 — From dredgings in all parts of the 

 lake ; most common on sand and on stony shore). — Six specimens, 

 two of which are quite young. The latter are winged posteriorly, 

 the beaks already eroded, and there are three to six nodulous 

 ridges descending in front of the umbo, nearly parallel to the 

 anterior margin ; they are concentrically finely thread-striated ; 

 colour olive-brown ; the inside is bluish-pearly, yellow under the 

 I icaks. The larger specimens are subventricose and thin, less 

 winged, the dorsal margin nearly parallel to the length-axis : 

 the beaks are corroded, the anterior margin rounded, sometimes 

 slightly truncate, the posterior margin produced and the ven- 

 tral margin broadly convex. The concentric striae are irregular, 

 rugose posteriorly, fine and more regular at the anterior end; 

 the marks of rest are fairly distinct. Most of the specimens are 

 partly covered with a dark-brown ferrugineous coating. In- 

 terior bluish, yellowish, or purple pearly, sometimes strongly 

 blotched with olive. Muscular scars shallow. Right valve 

 with two compressed triangular pseudocardinals close together, 

 the anterior tooth smaller, lamellar and smooth, the posterior 

 stronger, broader, and somewhat rugose. The lateral tooth is 

 slender, curved, rugose on the edge of the posterior part. Left 

 valve with two elongated, rounded, rugose pseudocardinals 



which s 'times coalesce, when only a slight notch indicates the 



original two teeth. The two laterals are long, slender, sinuate, 

 and distinctly pectinate at the posterior edges. There are always 



a tew small rather deep dorsal seal's in the umhonal cavity. 



