CEPHALOPODA. 



neighbourhood of London, including the identical specimen figured by Mr. Sowcrby. 

 Confining myself to external characters only, two distinct forms occur in this series, 

 the differences in which, although they may require a separation into varieties, are 

 not sufficient, in my opinion, for specific distinctions. 



In the first variety, which is the true Naut. zic-zac, figured in ' Mineral Conchology,' 

 and which I have therefore taken for the typical form, the shell is ventricose, the 

 greatest width being little less than half the diameter ; it is moderately round on the 

 ventral aspect, and the aperture is a somewhat elongated ellipsis. In the other variety (/3) 

 the shell is more compressed, almost discoidal ; and consequently it is narrower on 

 the ventral aspect; the dorsal lobes are not so broad, and the aperture is of a more 

 elongated oval form. 



The French, Belgian, and German shells correspond apparently with the first, the 

 typical form, and the Dax shells agree closely with the second variety. Michcllotti 

 has used for the Piedmontese specimens the specific description given by M. Deshayes ; 

 but he adds, that " they present some trifling differences from the Paris specimens, as 

 do the latter from the London and Bordeaux shells." As, however, the Piedmontese 

 shells arc described as " ventricose," they must for the present be referred to the 

 typical form, although we should naturally expect to find the Dax type continued in 

 the Miocene formations of the Colle de Torino. 



The Aturia zic-zac also occurs in the Miocene deposits in Malta, and the specimens 

 w T hich I have seen from that locality present the depressed form of the Daxshells, 

 with which they agree in other respects. 



Mr. Sowerby possesses a series of casts from the Eocene formation in Clarke 

 County, Alabama, of a species which approaches very near to the typical Aturia 

 zic-zac ; the chief distinction appears to be in the form of the lateral lobes, which in 

 the American shell extend quite to the margin of the preceding septa, and have their 

 extremities inflected towards the axis, and present the deep sinus which characterises 

 the lateral lobes of Naut. Parkinsoni. The siphuncle is very large, and corresponds 

 with that of A. zic-zac. Conrad describes his Pelagm Vanuxemi as more compressed 

 than the latter shell, and he adds that " the angles of the septa appear to be in contact 

 near the periphery." This appearance, which is attributable to the length of the 

 lateral lobes, and is represented in the figure given by Conrad by a continuous line 

 running parallel with the periphery of the shell, is also found in the Alabama specimens, 

 of which Conrad's shell is possibly only a compressed variety. 



The typical form, which is represented at Tab. IX, fig. la, \b, drawn from the original 

 specimen figured in ' Mineral Conchology,' for the use of which I am indebted to Mr. 

 Sowerby, is found at Highgate, Sheppy, and Bracklesham Bay. The variety /3, which 

 corresponds with the Dax shells, was obtained from the railroad cutting at Chalk 

 Farm, and from the well sunk for the use of the Orphan School, at Haverstock Hill, 



