226 DE. C. T. TRECHMAIs^?^^ OX [vol. Ixxili, 



widening sulcus, which extends to the apex and is bounded on 

 each side hj a shght, rounded, raised fold. The dorsal valve has a 

 strong, raised, roof-like, rapidly-\videning, triangular fold, which 

 extends to the beak and is bounded on both sides by a narrow 

 sulcus. The growth-lines are faint, but well marked. 



Length =18 mm. ; Avidth=20 mm. 



Locality and horizon. — The crest of Mount Heslington, 

 south of the Wairoa Grorge, in tine, brown, decomposed greywackes, 

 Avith Halohidd of the group of Halohia zitelJi. I collected 

 several specimens, both casts and moulds ; but it is not a common 

 form. Carnic. 



Kemarks. — This species forms the second group of Zugmayer's 

 Dimidiatse, in which the dental plates do not reach the back of 

 the ventral beak, but join the edge of the median septum where 

 it passes towards the area, forming a triangular sunken trough in 

 the areal region. This arrangement obtains also in the Palaeozoic 

 genus Cijrtina. from which Zugmayer separates his Dimidiata?, 

 apparently on account of differences in the delthyrium. He gives 

 a detailed description of Spiriferina suessi, which in the Alps 

 seems to be confined to the Koessen facies of the Rhsetic. The 

 New Zealand form appears to be slightly different in shape, 

 the sides meeting the hinge-area at almost a right angle ; but 

 the differences do not seem to warrant a new specific name for 

 it. A slight difference, however, is the presence on each side of 

 the delthja-ium of a very narrow, triangular, vertically- sulcate area, 

 Avhich Zugmayer says is absent in the Alpine Sp. stiessi, but occurs 

 in Sj). uncinata. I regard the present form as a local variety of 

 Sj)iriferina suessi. 



A drawing which Hector ^ published under the name of 

 ' Psioidea sp.' appears to represent this species. 



Spieifeeixa (?) CAEOLTX.E, sp. nov. (PI. XXIII, figs. 19«-20.) 



Yentral valve semi-pyramidal in shape, dorsal valve almost flat. 

 The hinge-line is straight, and represents the greatest width of the 

 shell ; the hinge-area is flat and vertical. The ventral beak is 

 conical and blunt, and does not project above the hinge-area. 

 The delthyrium is conical and apjDarently open. The hinge-area of 

 the dorsal valve is narroAv ; the dorsal beak is broad and blunt, 

 and projects but very slightly above the area. 



The ventral valve has a faint, shallow^ rapidly- widening, median 

 sulcus, which extends from the anterior margin to near the apex, 

 and on each side two very faint, shallow and broad, lateral sulci. 

 Otherwise the surface is gently rounded, and the outline of the 

 anterior margin is nearly semici]-cular. The dorsal valve, which is 

 nearly flat, bears a very faint, broad, low, median fold bounded by 

 scarcely perceptible lateral sulci. 



The interior of the ventral valve (tig. 19 a) shows two thick and 

 strong dental plates, which converge rapidly together and partl}^ 



1 Catal. Incl. & Col. Eslnbition (1886) p. 73, fig. 1. 



