part 3] JURASSIC ROCKS OP NEW ZEALAND. 273 



shell, which becomes rather flattened towards the margins, but 

 slopes steeply down to the posterior wing (which is devoid of ribs). 

 About fifteen radial ribs are present, which become rather stronger 

 and are gently curved on the anterior part. 



Dimension s. — Length = 24 mm. ; height = 21 mm. 



Locality. — Junction of Taylor's Creek and the Otapiri, Hoko- 

 nui Hills. Psiloceras Beds. 



Remarks. — The only specimen is a left valve with the shell 

 dissolved away. Other less perfect casts and impressions may 

 belong to the same form, but the condition of the material makes 

 it undesirable to attach a specific name to it. It seems to bear 

 some resemblance to a form described from Cretaceo-Jurassic 

 deposits of Queensland a*s 0. rockivoodensis R. Etheridge fil. 1 



OXYTOMA Sp. (PI. XIII, fig. 10.) 



Description. — A single left valve is gently and regularly 

 rounded," especially in the umbonal region. The beak is anterior, 

 and projects very slightly above the straight hinge-line. Behind 

 it there is a prolonged angular wing, well differentiated from the 

 rest of the shell. Below the wing the posterior margin of the shell 

 is considerably produced. The lower margin is gently rounded, 

 and the anterior margin is also gently rounded with hardly any 

 trace of an anterior projection. The ornamentation consists of 

 about eleven radial ribs that start from the umbo and pass to the 

 margins, where they are continued as short blunt prolongations. 

 All the ribs are rounded and rather faint, some more so than others, 

 and they are smaller and closer together on the anterior than on 

 the posterior portion of the shell. Very faint radial ribs are 

 intercalated between the main ribs. 



Dimensions. — Length = 34 mm.; length of hinge-area = 

 23 mm. ; height = 26 mm. 



Locality. — Southern shore of Kawhia Harbour, probably 

 Totara Point. 



Remarks. — It is useless to burden nomenclature with new 

 specific names for these shells. This valve, 2 which belongs to the 

 New Zealand Geological Survey, bears comparison with Avicula 

 cost at a Sowerb} r , a Bathonian species, of which Gottsche 3 figures 

 two casts of two left valves from Espinazito in the Andean 

 Cordillera. The beak in the New Zealand specimen is more 

 anterior than in either of Gottsche's figures, but this seems to be a 

 variable feature. 



Pterta cf. contorta Portlock. (PI. XII, fig. 10.) 



1843. 'Report on the Geology of Londonderry ' 2). 126 & pi. xxv A, fig. 16. 

 Description. — A single left valve, preserved as an internal cast 



: ' Geology & Palaeontology of Queensland ' 1892, p. 448 & pi. xxiv, fig. 15. 



2 It is apparently the original of a figure in J. Hector, ' Catal. Ind. & Col. 

 Exhibition' 1886, p. 69, labelled ' Avicula cynipes [sic] var.' 



8 ' Jura-Versteinerungen aus der Argentinischen Cordillera ' Paheontogra- 

 phica. Suppl. iii (1878) pi. vi, figs. 16 & 17. 



