230 DE. C. T. TRECHMANJ^- ON [vol. Ixxiil,. 



which, though scarcely adequate for a specific description, appear- 

 to represent a dwarfed species of Mentzeliopsis. These occur in 

 the Carnic with Halobia zitteli var, zealandica. 



Me?«^tzeliopsis spixosa, sp. nov. (PL XXIII, figs. 11-16.) 



The shell is slightly wider than it is long; the area is rather- 

 concave, less than the greatest width of the shell, and striated 

 parallel to the hinge-margin. The ventral valve is inflated and 

 arched ; the beak is prominent, tapers rapidly, and is rather bent' 

 over the area. The delthyrium is triangular and deepl}'^ sunken. 

 The ventral valve has a feeble, wide, median sulcus and very feeble 

 lateral dorsal folds. 



The dorsal valve is much flatter than the ventral, and has a 

 broad, rapidly-widening, triangular, slightly-raised fold, on each 

 side of which are about five very feeble, narrow, lateral folds. The- 

 growth-lines are rather widely spaced and foliaceous, and are some- 

 times produced into tubular spines. The latter also occupy the- 

 spaces between the growth-lines, but are not very closel}^ set. The}^ 

 attain a length of 3 or 4 millimetres. 



A ventral valve measures 19 mm. in length and 32 mm. in width ;; 

 another 25 mm. and 30 mm. ; two dorsal valves are respectively 

 20 mm. long and 31 mm. wide, and 20 mm. long and 26 mm. wide. 



Locality and horizon. — Kaihiku Beds at Caroline Cutting; 

 Kaihiku Gorge ; Eighty-Eight Valley, in the Nelson district ; and 

 other localities, where it is common. Ladino-Carnic. 



Remarks. — I collected most of my specimens at Caroline- 

 Cutting, and made several gutta-percha squeezes of the exterior- 

 and interior surfaces of both valves. 



Mentzeliopsis iioeeida, sp. nov. (PL XXIII, figs. 17 & 18.) 



Yalves rather inflated, both about equally so. Shell slightly 

 wider than it is long ; the ventral beak is broad, and tapers slowly.. 

 The ventral valve has a broad, shallow, median sulcus which reaches i 

 to £lie beak, and on each side of it about six rather faint, but 

 well-marked, rounded, narrow lateral folds, which also reach nearly 

 to the beak. 



The dorsal valve bears a rounded, triangular, rapidly- widening,, 

 median fold, Avith a smaller fold passing down the middle of it, and 

 four or five rather faint, lateral, rounded folds, all of which reach 

 to the beak. The spines are short, and small and closely set. 

 Growth-ridges are widely set and well marked, but not foliaceous. 



Length = 22 mm. ; Avidth = 26 mm. 



Locality and horizon. — -Kaihiku Beds at Caroline Cutting 

 and elsewhere, Avhere it seems to be scarce ; but I collected casts 

 from which gutta-percha squeezes of both valves Avere made. 

 Ladino-Carnic. 



Bemarks. — This form differs from J/, spinosa in having a 

 broader beak and a more inflated dorsal valve. The ribs are better- 

 marked and reach to the beak, and the spines are more numerous,, 

 smaller, and more closely set. 



