Thomson. — Geology of Middle Waipara and Weka Pass District, 383 



slightly produced. Valves moderately and regularly convex, folding very 

 slight. Beak suberect, not produced dorsally of the hinge-line, foramen 

 very large, mesothyrid, attrite, deltidial plates striate parallel to the hinge- 

 line. The septum shows no sign of transverse bands, so that the loop is 

 presumably Magellaniform. The cardinal process is of a primitive type, 

 confined to the posterior part of the hinge-trough. Length of holotype, 

 53 mm. ; breadth, 42 mm. ; thickness, 27 mm. 



The species is easily distinguished from other Neothyris by the size of 

 the foramen. 



Type locality : Creamy calcareous sandstone immediately following the 

 main Mount Brown limestone, Weka Pass, where it is common. 



Genus Stethothyris Thomson. 



Stethothyris sufflata (Tate). 



1880. Waldheimia (?) sufflata Tate, Trans. Roy. Soc. S. Austral., 

 vol. 3, pp. 157-58, pi. vii, fig. 3; pi. viii, fig. 4. 



1885. Magellania sufflata Hutt., Quart. Journ. Geol. Soc, vol. 41, 

 p. 558. 



1889. Magellania sufflata Tate, Trans. Roy. Soc. S. Austral., vol. 23, 

 p. 253. 



1905. Magellania siifflata Hutt., Trans. N.Z. Inst., vol. 37, pp. 476-77. 



Specimens from the uppermost Momit Brown limestone (E), thoiigh 

 showing considerable variation, agree ciosely enough externally with the 

 Australian species in shape, convexity, and folding, and in the incurvature 

 of the beak. In the last character senile individuals often show a beak 

 touching the dorsal valve, so that the pedicle must have atrophied.* The 

 cardinalia are characterized especially by the flattening of the ventral surface 

 of the socket-ridges anteriorly, the production of the crural bases into the 

 hinge-trough (seen in young specimens), and the swollen nature anteriorly of 

 the cardinal process, which, though large, is not very high. 



The characters of the beak and cardinal process suggest derivation from 

 a stock of considerable antiquity, and forbid its ascription to Neothyris, 

 which only appeared at this stage and did not attain similar characters 

 until a much later period in Neothyris lenticularis. The characters of the 

 cardinalia are not inconsistent with derivation from those of Stethothyris 

 uttleyi, and the shell shows the early sulcation of the dorsal valve exhibited 

 by ;S. pectoralis, so that the species seems best placed in Stethothyris. 



The species is common from the creamy calcareous sandstone following 

 the main Mount Brown limestone at the Weka Pass to the top of the 

 uppermost limestone, and is unknown elsewhere in New Zealand. 



PAET III.— CORRELATIONS AND THE CLASSIFICATION OF THE 



NOTOCENE. 



CLARENTIAN. * 



No beds belonging to this .division of the Notocene have been fomid in 

 the district, nor in the North Canterbury area. In this it differs from east 

 Marlborough, where the Amuri limestone is underlain by a great thickness 

 of Clarentian beds (c/. Thomson, 1919a). 



* Cf. BucKMAN, Pal. Ind., n.s., vol. 3, mem. 2, p. 17, 1917. 



