part 3] THE TKIAS OF NEW ZEALAND. 191 



Remarks. — This fonn agrees fairly well Avitli P. ^^rwacuta from 

 St. Cassian, but differs in having the beaks rather more anterior. 

 It comes nearest to Bittner's fig. 84, yet the differences hardly 

 seem to warrant a new specific name for it. 



Leda semicrenulata, sp. nov. (PL XXI, fig. 20.) 



Shell rather thick ; beaks broad and low, situated about the 

 middle of the shell, and directed slightly backwards. The anterior 

 margin is well rounded, the outline forming almost a semicircle ; 

 the lower posterior margin of the shell is produced upwards, and the 

 hinder part is rostrate. The decoration consists of about forty-five 

 rather sharp concentric ridges which are fairly regular on the 

 .anterior portion ; but near the beaks and on the posterior half, 

 though remaining constant in width, they become curiously wavy 

 and broken, producing a crenulated appearance. A blunt ridge 

 passes from the beaks to the lower end of the rostrate hinder 

 margin. Length := 18 mm. ; heights: 13 mm. 



Locality and horizon. — Bedc, Otamita (Hokonui Hills). I 

 collected two or three specimens with the shell on, but all rather 

 •crushed. 



Maceodon cf. cuEiONii Bittner. (PI. XXI, figs. 12 & 13.) 



1895. ' Lamellibranchiaten der Alpinen Trias ' p. 121 & pi. xv, fig. 16. 



Shell fairly thick. The hinge-margin is straight, and is pro- 

 duced in front of the beak, terminating rather sharply where it 

 joins the gently-curved and retreating anterior margin. About the 

 middle of the lower margin, which is nearlj^ straight, the shell 

 is contracted by a shallow sulcation extending almost to the 

 beak. The concentric growth-lines are well marked, but irregular. 

 Behind the beaks there is a faint trace of radial ribs inteirupted 

 by the growth-lines. Length=about 33 mm. ; height=:13 mm. 



Locality and horizon. — Bed c, Otamita (Hokonui Hills). I 

 collected a left valve there with the shell preserved, but damaged 

 itt both ends. The New Zealand Geological Survey possesses the 

 internal casts of two specimens from Mount Heslington (Nelson), 

 showing the characteristic dentition ; but they are not specifically 

 determinable, though probably belonging to the same species. 

 ■Carnic. 



Remarks. — At least one species of Macrodon occurs in the 

 New Zealand Trias, but the shells are scarce. My specimen 

 resembles rather closely the above-named species from the Raibl 

 Beds of Lake Iseo (Lombardy). It recalls also a closely-related 

 form, M. esinensis Stoppani, from the Esino Limestone, which 

 Bittner figures on the same plate, figs. 17 & 18. 



PSEUD0:\I0N0TIS AND MONOTIS. 



The Monotis-\\k^ shells, which Hochstetter brought from Rich- 

 mond, near Nelson, were identified by Zittel as a variety of 

 Jlouotis salinaria and called var. ricltinondiana. The fact that 



