part 3J JURASSIC ROCKS OF NEW ZEALAND. 267 



Aucella spitiensis cf. var. Extensa Holdhaus. (PL XIV, 

 figs. 5 & 6.) 



1913. 'Fauna of the Spiti Shales (Laniellibranchiata & Gasteropoda) ' Pal. Ind. 

 ser. 15, vol. iv, p. 408 & pi. xcvii, figs. 7-13. 



Description. — Outline elongate oval, not very oblique. The 

 beak is very anteriorly situated, almost terminal, strongly arched 

 and rounded, in some examples nearly hemispherical, slightly 

 bent over the hinge-line. The anterior umbonal portion of the 

 valve is rounded and swollen, but towards the posterior and lower 

 part it becomes flattened out. The surface is irregular, and bears 

 several wide and shallow irregular concentric furrows, especially 

 noticeable on the flatter parts. A broad depression occurs below 

 the beak, some little distance from the lower anterior margin. 

 The hinge-margin is straight or slightly bent, and the lower 

 margin runs almost parallel with it ; the posterior margin is well 

 rounded, the anterior narrowly rounded ; growth-lines are irre- 

 gular, but well marked. The right valve is much flatter than the 

 left, but is still well rounded ; the beak is not generally raised 

 above the surface of the valve, and traces of a small anterior ear 

 are perceptible below it. The surface is marked with irregular, 

 shallow, concentric growth-furrows. The shell in both valves is 

 thin, and platy in structure. 



Dimensions. — Leftvalve: length = 52 mm.; height=20 mm.; 

 depth = 15 mm. Right valve : length = 51 mm. ; height=20 mm. 



Locality and horizon. — Waikato, South Heads (North 

 Island). Several examples were collected by Prof. P. Marshall 

 and Mr. J. A. B-artrum. Upper Jurassic. 



Remarks. — The left valve agrees closely with Holdhaus's 

 pi. xcvii, fig. 12 a. The right valve, although more elongated, 

 bears comparison with fig. 9. 



Aucella spitiensis cf. 'forma typica.' (PL XIV, fig. 7.) 



Description. — In the left valve the beak is anterior, but not 

 cmite terminal, not very prominent, rounded, and only slightly 

 bent over the hinge-area. The hinge-margin is very slightly 

 arched, the posterior margin broadly rounded (almost semicircular), 

 the lower anterior margin gently curved, the anterior margin 

 narrowly rounded. The whole surface of the shell is gently 

 rounded, and is not marked by any irregular concentric furrows, 

 except a very shallow scarcely perceptible one, almost midway 

 from the beak to the lower anterior margin. 



The left valve is decorated with a number of prominent, irregu- 

 larly-spaced, rather wavy growth-ridges, which become distinctly 

 foliaceous. They are widest apart in the umbonal region, but 

 become rather crowded together towards the margins, and enclose 

 shallow sulci between them. 



The right valve is raised and rather flattened towards the beak, 

 but becomes nearly flat posteriorly. It agrees in ornamentation 



