The Belemnoidea, ranging from the Trias to Eocene, comprise the extinct Belemnites, the interesting genus Spirulirostra of Miocene times, and the living Spirula.
Sepioidea.—
The Sepioidea or true Cuttle-fishes (“pen-and-ink fish”) range from the Trias to the present day.
Octopoda.—
The Octopoda, with Octopus and Argonauta (the paper “Nautilus”) are present-day modifications. The male of the latter is without a shell, the female only being provided with a delicate boat-shaped shell secreted by the mantle and the two fin-like expansions of the dorsal arms.
Ordovician Cephalopods.—
The Ordovician cephalopods of Australasia are not numerous, and are, so far as known, practically restricted to the limestones of the Larapintine series at Laurie’s Creek and Tempe Downs, in Central South Australia. Amongst them may be mentioned Endoceras warburtoni ([Fig. 105 A]), (a straight form in which the siphuncle is partially filled with organic deposits); Orthoceras gossei; O. ibiciforme; Trochoceras reticostatum (a coiled form); and Actinoceras tatei (a genus characterised by swollen siphuncular beads between the septa).
Fig. 105—PALAEOZOIC CEPHALOPODA.
