278 DR. C. T. TBECHMAU-ff ON THE [vol. lxxix, 



anterior margin downwards and backwards ; where they meet the 

 larger ribs they form an acutely angular V-shaped decoration, 

 which is specially marked in that part of the shell that lies just 

 below and behind the beak. 



All the ribs are more or less cut by the growth-lines, which are 

 sharp and regular, forming a finely nodose ornamentation in front 

 of the primary ribs in the lower half of the valve. The nodes 

 often conjoin, and become elongated in the direction of the 

 growth-lines. Nothing of the dentition could be seen. 



Dimensions. — Length=21 mm.; height = 18 mm.; another 

 specimen is 18 mm. long and 12 mm. high. 



Locality and horizon. — Southern shore, Kawhia Harbour. 

 All the specimens belong to the New Zealand Geological Survey. 



I did not find any ; but, as several species of fossils that 

 Prof. Marshall and I collected at Totara Point occur in the same 

 pieces of rock with them and the matrix is similar, it seems that 

 these Trigonias are from some exposure at or very near Totara 

 Point. 



Remarks. — These Trigonias generally are poorly preserved; 

 but, by dissolving the shell with weak acid from the cavities in 

 the fine-grained greywacke, and making gutta-percha squeezes, 

 one can recover the rather complicated surface-ornamentation. 



They belong to a group of which several forms have been 

 described from the Bathonian and Lower Oolite of Espinazito in the 

 Argentine Cordillera. These are Trigonia prcelonga Gottsche ; 

 T. rectangular is Gottsche; T. lycetti Gottsche; T. signata 

 Agassiz x ; T. exotica Steinmann ; and T. gottschei Moricke. 2 



The New Zealand form is rather similar in some ways to 

 T. lycetti from the Lower Oolite of Espinazito, but is much 

 smaller than the largest specimens of that species, which has two 

 furrows on the areal region. The nature of the ribs that spring 

 from the main ridge also is different. 



In shape it rather resembles T. exotica ; but the number of ribs 

 in that species is less, they are broken up into larger nodes, and 

 the Y-shaped decoration is less strongly marked. 



The South American form which it most closely resembles in 

 ornament is T. gottschei ; but that is a very much more elongate 

 shell, and has two furrows passing down the area as in T. lycetti, 

 while the shell here described has only one. 



T. rectangularis is a shell that agrees in general size and out- 

 line with the New Zealand form ; but the decoration is much 

 simpler, and the V-shaped costation is much less acutely angular, 

 being practically a right angle. 



The decoration of all these Trigonias refers them to the group 

 of the Undulatse, of which two of the best-known members are 

 T. literata Young & Bird, from the jurensis zone of Yorkshire, 



1 C. Gottsche, ' Ueber Jura-Versteinerungen aus der Argentinischen 

 Cordillera' Palaeontographica, Suppl. iii (1878) pp. 24-27 & pi. vi. 



2 W. Moricke, ' Versteinerungen des Lias & Unteroolith von Chile ' Neues 

 Jahrb. 1894, pi. vi, figs. 7-9, 



