Maitai Series of New Zealand. 57 



opinion, for the following reasons among others, that it belongs to the 

 Myalinid genus Aphanaia, 1 de Kon., two species of which have been 

 described from the Permo-Carboniferous of Australia : — 



1. The type-specimens of the genus described by de Koninck were 

 only casts, and consequently, as he remarks, the structure of the shell 

 could not be ascertained. However, I obtained during the British 

 Association excursion to the Maitland Coalfield in 1914, a specimen 

 of Aphanaia cf. Mitchelli, from the lower marine beds of Harpers 

 Hill, New South Wales. This specimen has the two valves in 

 apposition, and is damaged, but part of the hinge and portions of the 

 shell remain. The shell is prismatic in structure as it is in the case 

 of the New Zealand fossil, and is made up of rows of upright prisms 

 standing at right angles to the surface of the valves just as is the case 

 in Pinna or Inoceramus. 



2. The shape of the shell agrees with that of Aphanaia. The 

 beaks of Aphanaia are anterior or terminal, and in one species are 

 described as recurved. The hinge-line is straight or slightly bent 

 and makes practically a right angle with, the anterior margin of the 

 shell, and there is no trace of an anterior ear. These features apply 

 equally well to the New Zealand fossil. 



The fact of de Koninck' s original specimens being casts makes 

 a close comparison a matter of some uncertainty, but apart from 

 this the only thing which would cause me to hesitate in this 

 attribution is that I have not been able to see the muscle-scars in the 

 New Zealand shell. These in the Australian forms are said to be 

 very large and pronounced, but the shells I collected at Wooded Peak 

 are so crushed and fractured that the muscle impressions seem 

 to have become obliterated. Only the harder and thicker region 

 of the beaks remains more or less unbroken in the rock ; the rest 

 of the large and thin shell is crushed into small pieces, which, 

 however, are not displaced to any extent. 



1 only found the separated valves at Wooded Peak, but obtained 

 specimens from which I Avas able to make gutta-percha squeezes 

 of the beak and hinge area of both right and left valves. Among the 

 specimens which Mr. McKay collected, however, there is one which 

 has the apex of the opposite valve in position, but I cannot say if the 

 two valves were equal in size or not. The largest specimen 

 I collected measures 170 mm. long and 95 mm. high. The beaks 

 are rounded or boss-like, are nearly or quite terminal, recurved 

 so as to face one another and stand straight above the anterior end of 

 the hinge- line. The hinge area is broad and long, and is marked 

 by shallow parallel longitudinal grooves separated by almost equally 

 wide ridges. 2 The hinge-line forms an obtuse rounded angle with 

 the posterior part of the shell, but a right angle with the anterior 

 margin. The anterior portion of both valves in front of and below 

 the beaks is folded inwards, and there appears to be a retreat of 



3 Descriptions of the Palceozoic Fossils of New South Wales, Eng. trans. 

 (Mem. Geol. Surv. N.S.W.), Paleontology, No. 6, 1898, p. 238, pi. xxi, 

 figs. 5, 6. 



2 This structure is, of course, quite different from that of Inoceramus, which 

 has a row of vertical ligament pits on the area. 



