Nautilus ziczac. 



533 



66 



The sinuous 



session of this gentleman is truly splendid : the specimens of 

 several species exhibiting every gradation of size from an ex- 

 tremely young state up to the adult period. 



The specimen here figured (Jig, 66.), certainly the rarest and 

 most interesting of the species of this genus which occur in the 

 London clay, he procured from the tunnel at Primrose Hill. 

 In the Mineral Conchology, we 

 find at tab. 1. fig. 4«. a represent- 

 ation of an imperfect specimen 

 of this truly elegant fossil, 

 under the name of Nautilus 

 ziczac ; but Mr. Sowerby does 

 not notice the remarkable cha- 

 racter of its chambers, except as 

 a ready means of distinguishing the species 

 septa, so beautifully shown in this specimen, from the loss of 

 the external coat, would place this species in that division of 

 fossil multilocular shells to which the term Goniatite has been 

 applied by Von Buch, were not the siphunculus placed along 

 the internal margin. The characters of this shell, indeed, will 

 not admit of its being placed in either the genus Nautilus or 

 Ammonites, as will be seen by a reference to the following 

 characters of the families Nautilida? and Ammonitida?, in the 

 article Cephalopoda, by Mr. Owen, recently published in 

 Todd's Cyclopaedia of Anatomy and Physiology : — 



Fam. 1. Nautilidne. Shell external, spiral or straight; septa smooth, 

 simple ; the last chamber the largest, and containing the animal ; siphon 

 central or marginal and internal. 



Fam. 2. Ammonitidae. Shell external, spiral or straight ; septa sinuous 

 and with lobated margins ; the last chamber the largest, and lodging the 

 animal ; siphon central or marginal and external. 



Now, it is clear, that the specimen before us is neither 

 Nautilus nor Ammonite; for we are here presented with 

 sinuous septa, whilst the siph uncle is marginal and internal. 



The following may be given as its characters : — 



Shell involute ; inner whorls concealed as in Nautilus ; septa witli 

 deep lateral narrow sinuosities ; siphuncle continuous, marginal, and in- 

 ternal. 



These characters might, perhaps, be thought by some suffi- 

 ciently tangible to establish a genus for the reception of Nau- 

 tilus ziczac ; but I should not consider myself warranted in 

 so doing, because I am aware of the existence of a fossil also 

 from the London clay, and which is figured by Mr. Parkinson 

 (Organic Remains, vol. iii.), in which the septa are like those 

 of N. ziczac, but the siphuncle is not marginal. This speci- 

 men, which is of large size, is now in the possession of Mr. 



