588 



MOLLUSCA 



PHYLUM VI 



Nautiloid shells or detached. The jaws belonging to Nautilus bidorsahis froni 

 the Trias were originally described under the name of Rhyncholites and 



A i: 



Upper jaw of NaiUilus pompiliiis. 

 A, Side view ; li, Inferior aspect, i/i. 



Fin. 1100. 



Lower jaw'of Mufii^ws 

 jMinpilius. Side view. i/j. 



Fir,. 1101. 



Temnoclicihis hidorsatus Schlotli. ( = ii/ii/H- 

 chfiUthcs hirmulo Faure-Bignet). Musciiel- 

 kalk ; Lainecl<, near Bayreutli. A, Upper 

 jaw, viewed from above ; B, from tlie .side ; 

 C, from below. 



Conchorhyncliiis (Figs. 1101, 1102); the common Jurassic and Cretaceous 

 forms are known as Ehymhoteuthis (Fig. 1103) and Palaeoteuthis d'Orbigny. 

 The long feather-like gills are disposed in two pairs at the base of the 

 hyponome, and between them is the anus, closely behind Avhich is placed the 



A single or double orifice 



of the generative or- 

 gans. In the female 

 there is found at the 

 base of the gill cavity 

 a long, tri- 

 partite, nida- 

 mental gland, 

 which fuses 

 externally 

 with the 

 mantle. 



The body 

 is short, 

 sack - shaped, 

 rounded pos- 

 teriorly, and enveloped by the mantle. The base of the latter is prolonged 

 at a certain point into a fleshy, hollow cord or tube (the siphon), which passes 

 through a rounded aperture in each of the septa, and extends as far as the 

 inner side of the apex in the initial chamber. The fastening of the animal 

 within the living chamber is accomplished by two oval muscles situated on 

 either side near the base of the mantle. These muscles are attached to the 

 inner wall of the living chamber, and have corresponding but very shallow 

 impressions. They are connected both dorsally and ventrally by a band of 

 fibres, the annulus, which also leaves its impression upon the shell. The form 

 and position of the muscles for attachment and the annulus are sometimes 

 discernible on the internal moulds of fossil shells. 



The shells of existing Nautili are coiled in one plane, and composed of 

 several volutions, the outermost of which either envelops all the earlier ones 

 {Nautilus fompilius), or leaves the umbilicus partly open {N. umhilicatus). 



Fig. 1102. 



Temnocheilus hidorsatus Schlotheim 

 (= Conchorhynchus avirostris Blainville). 

 MiLschellcalli ; Laineck, neap Bayrenth. 

 Lower jaw viewed from above. 



Rhynchoteuthis sahaudianus Pict. and Lor. 

 Neocomian ; Voirons, France. A, Dorsal 

 aspect, showing in part the chitinous lateral 

 expansions. B, The calcareous beak seen 

 from below. 



