OLIVER : NEW ZEALAND PELECYPODS. 181 



reach a length of 28 mm., and have in the central and dorsal portion 

 of the left valve a large green patch showing both inside and outside. 



4. Mytilus planulatus, Lamarck. 

 Mytilus planulatus, Lamarck, 1819, Anim. s. Vert,, vol. vi, pt. 1, 



p. 125. 

 Mytilus edulis (not Linne), Hutton, 1880, Man. N.Z. Moll, p. 167 ; 

 Suter, 1913, Man. N.Z. Moll., p. 862, pi. Ivi, fig. 4. 



For more than forty years the common mussel of the southern 

 portion of New Zealand has been masquerading under the name of 

 M. edulis of the Arctic and north temperate regions. This is the 

 more strange because the species to which it belongs was, on 

 Australian specimens, recognized as distinct from the northern 

 species by Lamarck over 100 years ago, and, judging by the 

 synonyms, by several other authors subsequently. The type is 

 from King George's Sound, Western Australia, and the species occurs 

 from there eastward to New South Wales and Tasmania. In New 

 Zealand it is the most common mussel found between tide-marks 

 from Cook Strait southward, and it is also found at Great Barrier 

 Island. The true M. edulis has an expanded lip, or hinge-plate, bear- 

 ing a row of small teeth, usually four to six in number. The colour of 

 the shell is bluish- to brownish-black, with radiating blue lines. 

 These latter are best seen on young shells, but many old ones also 

 show them. The New Zealand shell is much thicker and heavier, 

 and has only two or three teeth, larger than in M. edulis and placed 

 inside the apex, not on an expanded lip. The colour is bluish- 

 black weathering to blue, and there are never any radiating bands. 

 It is thus easily separated from M. edulis, but I have failed to find 

 any character by which it can be distinguished from M. planulatus. 



M. planulatus from Cook Strait southward forms extensive 

 associations on rocks in the mid-tide belt. In size it appears to 

 increase from north to south. For instance, the average length of 

 the shell in Wellington Harbour is 65 mm., in Stewart Island shells 

 of 75 mm. in length are common, while Suter states that specimens 

 from the islands to the south of New Zealand are of a very large 

 size. The largest specimens I have seen, however, came from Great 

 Barrier Island, north of Auckland, and measured 89 mm. in length. 



5. Modiolus confusus (Angas). 

 Perna confusa, Angas, 1871, Proc. Zool. Soc, p. 21, pi. i, fig. 21. 

 Modiolus fluviatilis, Hutton, 1878, Journ. de Conchyl., p. 53 ; Suter, 

 1913, Man. N.Z. Moll., p. 867, pi. clviii, fig. 6. 

 Modiolus confusxis is an Australian species from which I am 

 unable to distinguish M. fluviatilis of Hutton. In both countries 

 the species occurs in brackish water, and is variable in the shape of 

 the shells. Both Mr. May, of Tasmania, and Mr. Hedley, of Sydney^ 

 are in agreement with me in uniting the Australian and New 

 Zealand forms under one name. 



