IKTRODrCTION. 
XTll 
represented in North America, Belgium, and Ireland. The other 
genera, extant in the Devonian, continued to exist, though in very 
much diminished numbers. 
The works of de Koninck ^ Phillips % and M‘Coy have made us 
acquainted with a great number of forms more or less closely 
related to Xautilus. De Koninck records 52 species from Belgium, 
amongst which are included several of those described by M‘Coy, 
Phillips, J. Sowerby, and J. de C. Sowerby. 
The genera Orihoceras, Ci/i’toceras, and Gyroceras now exhibit a 
marked decline in the number of their species. In the Permian 
(Dyas) of Germany only 3 species of OrtJioceras, 1 of Cyrtoceras (?), 
and 5 of Xautilus’' (including species belonging to the genera 
Pleuronautilus, Mojs., and Pteronautilus, Meek) are recorded \ In 
the “Salt-Eange” (Productus -Limestone, of AVyune) of India®, 
Dr. W. Waagen has described 10 species of Natdihis'^ {Pleuro- 
nautilus,’^ Mojs.), 1 of Gyroceras (admittedly doubtful), and 4 of 
Orthoceras (one undetermined). Mojsisovics ® records, in his work 
upon the Trias of Germany (Med. Triasprov.), 19 species of 
Nautilus (Cenoceras, Hyatt, pars), 5 species of Temnoclieihis, 
3 of TrematofUscus, and 7 of Orthoceras (one undetermined). 
It is impossible not to be struck with the apparently sudden 
extinction of Orthoceras. One of the species {Orth, campanile^ from 
the Trias) described by Mojsisovics might well be compared for 
perfection of development with any of the most typical of its 
precursors in the Palaeozoic rocks ; nevertheless, so far as we know, 
it was one of the last of its race'. 
In the search for connecting-links between the Nautiloidea and 
Ammonoidea our attention is arrested by the peculiar form 
Bactrites, which, though probably a true Nautiloid'* *, is connected 
^ ‘ Faune du Calc. Carb. fie la Belgique,’ 1878, prem. partie, “ PoisBons et 
genre ?sautile.” 
^ ‘Geology of Yorkshire,’ 1836, pt. ii. 
* ‘ Synop. of the Carb. Foss, of Ireland,’ 1844, ami ‘British Pal. Foss.’ fasc. 
i.-iii., 1852-1855. 
*■ Zittel, ‘ Hanclb. cler Palaeontologie,’ 1884, p. 387 ; Creclner, ‘ Elemente der 
Oeologie,’ 1887, p. 508. 
® Mem. Geol. Surv. India — Palaeontologia Indica, 1879, Ser. xiii., i. 
® “ Die Cephalopoden der Mediterranen Triasprovinz,” in Abhandl. d. k,-k. 
Geol. Reich-sanst. 1882. 
The well-known case of Lingula may also be cited as an example of the 
extraordinary persistence of certain types. 
® Hyatt, Proc. Boston Soc. Nat. Hist. 1883, vol. xiii. p. 303. 
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