Sutek. — On New Zealand Mollu&ca. 



239 



cimens 



F,p 2 



FTg.3 



Diplodon menziesi, Gray, n. subsp. lucasi. 



Lake Manapouri (Stat. 35 — Dredging in 60 ft.). — Three spe- 

 one of them may be taken as adult. Shell (figs. 2 

 and 3) oblong-ovate, very much compressed, thin and fragile, 



inequilateral, beaks 

 low, eroded ; surface 

 with close strongly 

 pronounced rest- 

 marks and between 

 them a few lines of 

 growth, all close to- 

 gether and foliated 

 at the anterior end. 

 In the adult speci- 

 men the middle part 

 has distinct radiate 

 nodulous sculpture, 

 partly V-shaped, but no such ornamentation is to be found on 

 the young specimens. The straight dorsal margin is subparallel 

 to the ventral margin, which is slightly sinuate ; the anterior 

 margin is angularly rounded, the posterior obliquely truncated 

 and slightly produced. Nearly the whole of the shell is covered 

 with a thin ferrugineous coating ; the epidemis is olive-green, 

 waxy. The ligament is small, not much raised. In the right 

 valve the two pseudocardinals are compressed, small ; the upper 

 anterior tooth is a small, smooth lamella, the lower tooth is more 

 elevated, conoidal, and strongly crenate ; the lateral tooth is 

 almost straight, thin and rugose at its posterior portion. In 

 the left valve there is a rather long compressed lower anterior 

 rugose pseudocardinal, the upper tooth is quite rudimentary ; 

 the upper lateral tooth is a little higher and more rugose pos- 

 teriorly than the other. Interior bluish-white, pearly, a little 

 blotched with olive in the umbonal cavity, where there are 

 rather large and deep dorsal scars. The adductor-muscle scars 

 are shallow. The young specimens are slightly winged. 



This subspecies is nearest to the typical aucklandica, but is 

 distinguished from it by its exceptionally compressed form, the 

 thinness of the shell, the strongly marked and close concentric 

 lines, the more tapering posterior margin, and the feebly developed 

 pseudocardinals. The radiate nodulous sculpture is found in 

 many specimens of menziesi and its subspecies. Adult specimen 

 — Length, 45 mm. ; height, 24 mm. ; diam., 8 mm. 

 Type in my collection. 



I have much pleasure in naming the subspecies in honour of 

 its discoverer, Mr. Keith Lucas. 



