Tertiary.-i PALEONTOLOGY OF VICTORIA. [Mollusca. 



Plate XXIV., Fios. 1-5. 

 ATURIA ZIC-ZAC (Sow. sp.). Var. AUSTRALIS (McCoy), 



[Genus ATURIA (Bronn). (Sub.-kingd. MoUusca. Class Cephalopoda. Order Tetra- 

 branchiata. Fam. Nautilidaj.) 



Gen. Char. — Shell, discoid, moderately compressed, periphery rounded, whorls embracing, 

 inrolute in one plane ; septa convex outwardly at inner half, concave at outer half, bent on 

 each side at the margin into a long narrow lancet-shaped lobe extending backwards to the 

 preceding septum ; siphuncle at inner margin very large, shelly, formed of a funnel-shaped 

 extension backwards of the septum, the narrow hinder end entering within the similar funnels 

 of the two preceding septa.] 



Description. — Sides flattened ; periphery narrow, rounded; surface with fine 

 arched stria, the convexity forwards on the sides, backwards on the periphery. 

 Diameter, from 1 to 4^ inches ; proportional g'reatest width, -^^^ ; length of aperture 

 at side, -f^^ ; at middle, -^^-j^. 



Tlie great shelly invaginated siphuncle easily distinguishes 

 Aturia from Nautilus as well as the position of the siphon at the 

 inner margin ; and as Nautilus extends fi'om Palseozoic times to our 

 present seas, while Aturia is only found in the Eocene and Miocene 

 strata of other parts of the world, a recognition of the structural 

 difference between the genera is of great geological interest, as 

 supporting the suggestion of the Oligocene age of the Tertiary 

 strata in Victoria, in which it is so surprising to find this rare t3'pe 

 of Cephalopoda peculiar to the Middle and Lower Tertiaries of the 

 old world and of America. 



It is with the compressed Miocene variety found at Dax, named 

 N. Aturiahj Basterot, rather than with the more ventricose original 

 types of the N. zic-zac of Sowerby, proper to the Eocene Loudon 

 clay, that our Australian fossil more completely agrees ; and I can 

 only doubtfully suggest the separation of it as a local variety, from 

 the somewhat greater compression indicated by the slightly greater 

 length of the aperture in proportion to its width ; and also a 

 slightly greater curvature of the septa on the sides as shown by a 

 line from the apex of the lancet-shaped lobe to the inner end of 

 same septum, encroaching rather more on the 3rd chamber behind. 



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