BUB-CLASS I 



TETRABRANCHIATA 



horny substance, only their points being calcified. Similar calcified beaks are 

 not uncommon in Mesozoic terranes, being found either associated with N.-niti- 

 loid shells or detached. The jaws belonging to Temnocheilus bidormtus from 



FIG. 1050. 



rpjxT jaw of Xmitiliix j,i,i,ij,;Hit.<. 

 A, Side view. B, Inferior aspect. 1/1- 



FI.J. 1051. 



Lower jawcif Xinit 

 pompiliu*, siile view. i 



Fi... 1 1 :._'. 



Ternno 



r7,/;//'s Mr-undo, Faiuv-i;j : .:m-n. M 

 k:ilk; Laineok. in-ar Hayn-utli. A, Upper 

 jaw, viewed from above. B, from the side. 

 C, from below. 



the Trias were originally described under the name of Rhynclwlites and 

 I'lHirJiorhynchus (Figs. 1052, 1053); the common Jurassic and Cretaceous 

 forms are known as Rhynchoteuthis (Fig. 1054) 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 which is placed 

 the single or double 

 orifice of the generative 

 organs. In the female 

 there is found 

 at the base of 

 the gill cavity 

 a long, tri- 

 partite, nida- 

 mental gland, 

 which fuses 



FIG. 1054. 



Temnocheilus faVr.>"'"s Hchloth. 

 ( = C'onchorht/nchus avirostris, Blainv.). 

 Muschelkalk ; Laineck, near Bayretith. 

 Lower jaw viewed from above. 



;> Siilm mlin mis, Pict. and Lor. 



Xeoeomian ; Voirons, France. A, Dorsal externally 

 aspect, showing in part the chitinous lateral 

 expansions. B, The calcareous beak seen 

 from below. 



with 

 mantle. 



the 



The body is short, sack-shaped, rounded posteriorly, 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 casts of fossil 

 shells. 



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



