270 
NAUTILOIDEA, 
compared with the total length of the shell. The curvature of the 
latter is generally slight. The group contains both longicone and 
brevicone species, and ranges from the Cambrian to the Carboni- 
ferous. 
CAMBEIAN SPECIES. 
Cyrtoceras (Meloceras) praecox, Salter, sp. 
1866. Cyrtoceras prcecox, Salter, Memoirs of the Geol. Surv. vol. iii. 
p. 358, pi. X. f. 3. 
1872. Cyrtoceras prcecox^ Salter, in Murchison's ‘Siluria,’ 5th ed. 
p. 535. 
1882. Cyrtoceras prcecox, Blake, British Foss. Ceph. pt. i. p. 166, 
pi. xviii. ff. 6, 7. 
Sp, Char. “About an inch long, conical, gently curved, the 
mouth very oblique, the inner (dorsal ?) margin being the prominent 
one. The septa, which follow the same curve, from within outwards, 
are placed very near together, four chambers in the space of of 
an inch.” (Salter.) 
The specimen in the British Museum is thus described by Prof. 
Blake : — “ 17o section is seen; the curvature has a mean radius of 
3^ inches. The rate of increase is about 1 in 4. Across the surface 
are a number of parallel folds ; hut whether they are folds of growth, 
and the deeper lines the septa, or whether they are merely due to 
the tension of the material, cannot be determined.” The position of 
the siphuncle is unknown. 
Remarhs. Prof. Blake cautiously observes that these two specimens 
may not belong to one species. Salter notices the interesting fact 
that Cyrtoceras prcecox the earliest Cephalopod known, and says 
that “ it is not a little remarkable that the first species we meet 
with in ascending order should he — not Orihoceras, which is the 
most difiused and persistent form, but a genus which, so far as we 
know, is only Silurian [the term is here used to include Cambrian, 
Ordovician, and Silurian] and Devonian.” 
Horizon. Upper Tremadoc. 
Locality. Garth, near Portmadoc, Carnarvonshire. 
Eepresented by the example figured by Blake (loc. cit. f. 6). 
OEDOYICIAN SPECIES. 
Cyrtoceras (Meloceras) falx, BiEings, sp. 
1857. Cyrtoceras falx, Bilhngs, Geol. Surv. of Canada, Eep. of Pro- 
gress for the years 1853-56, p. 314. 
