19S DE. C. T. TRECHMAN]S" OlS [vol. Ixxiii^ 



very faint, raised, loundecl liius, Avhieli are produced i-egularly 

 downwards and backwards with a slight anteriorly-eoncav(} beiui. 

 Some distance below the beak they widen out, become wavy, and 

 bend suddenly forwards, continue thus for a short distance and then 

 bend downwards again less abruptly, passing towards the lower 

 and anterior margins. In some specimens the hinder portion of 

 the shell is almost smooth, in others the ribs continue in fairly- 

 straight though wavy lines, between which a series of shallow 

 furrows of very irregular width are produced. On the anterior ear 

 the faint radial ribs are sometimes seen on the portion bordering 

 the hinge-line. Concentric growth- ripples are well marked in the 

 region of the beak, but are broad, shallow, and irregular in width. 

 They are also developed on the anterior ear, but to a less extent. 

 Secjondar}'' ribs appear intercalated between the primary ribs on 

 the posterior portion of fully-grown shells. The marginal outline 

 is difficult to construct, as the shells are nearly always im- 

 perfect ; but the anterior ear projects beyond the lower anterior 

 margin and is well rounded, and the margin retreats below it, at 

 least in the right valve. Under the ear the margin is well rounded,^ 

 the lower margin seems fairh^ straight or gently rounded, and the 

 posterior margin broadly rounded. 



This species attains a large size ; the biggest example that I col- 

 lected, when perfect, must have measured about G5 mm. in length 

 and 42 mm. in height. 



Locality and horizon. — Large specimens are rather common 

 in brown, decomposed, fine-grained greywackes on the crest and 

 saddle of Mount Heslington, south of the Wairoa Gorge, Nelson. 

 It occurs also in Bed e in the Otamita section, Hokonui Hills, and. 

 I found some small examples in hard greywackes at Xugget Point,, 

 above the H/ftil/is-jn-ohlejuaficifs Bed. I collected specimens in 

 various stages of growth in all these localities. Carnic. 



Eemarks. — This large and variable JIaJohia falls into the 

 group of li. faJJax of 1he classification of Mojsisovics. The New- 

 Zealand form seems to partake of the characters, both of H. zitfeli 

 Lindstrom and of H. superha Mojsisovics. The sudden forward 

 bending of the ribs occurs nearer the beak than in H. siiperha, but 

 somewhat farther away than in H. zitfeli. The ribs are less- 

 numerous than in H. superhct, but the}^ become wavy in the 

 anterior portion of the shell, which seems not to be the case in 

 H. zitfeli. However, the form here described seems to be nearer- 

 to H. zitfeli than to H. superha^ and I am inclined to regard it 

 as a local variety of the former species. 



H. zitfeli comes from the Trias of Spitsbergen, where it occurs- 

 in rather high Camic beds with Pinacoceras cf. JJoriJum. It 

 also occurs in the Upper Trias of Bear Island, and some forms- 

 figured as young examples from both these localities closely 

 resemble some of the Halobias from New Zealand. H. mperha 

 occurs in the Carnic of the Austrian Alps. 



