SUB-CLASS I TETRABRANCHIATA 507 
horny substance, only their points being calcified. Similar calcified beaks are 
not uncommon in Mesozoic terranes, being found either associated with Nauti- 
loid shells or detached. The jaws belonging to Temnocheilus bidorsatus from 
A 

Fic. 1052. 
Temnocheilus bidorsatus, Schloth. (= Rhyn- 
cholithes hirundo, Faure-Biguet). Muschel- 

1G. 1050. :. 105 : 
2 z 4 peo T te kalk; Laineck, near Bayreuth. A, Upper 
Upper 10% of Nautilus pompilius. Lower jaw of Nautilus jaw, viewed from above. B, from the side. 
A, Side view. LB, Inferioraspect. 1/;. —_pompilius, side view, 1/}. C, from below. 
the Trias were originally described under the name of Lhyncholites and 
Conchorhynchus (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. 
Fic. 1053. 
Temnocheilus bidorsatus, Schloth. Neocomian ;. Voirons, France. A, Dorsal externa 1] Vy 
Rhynchoteuthis Sabaudianus, Pict. and Lor. 
(=Conchorhynchus avirostris, Blainv.). aspect, showing in part the chitinous lateral C 
Muschelkalk ; Laineck, near Bayreuth. expansions. B, The caleareous beak seen W 1 th the 
Lower jaw viewed from above. from below. mantle 
c } . 
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 
