SPIRULID. 49 
Shell placed vertically in the posterior part of the body, with 
the involute spire towards the ventral side. 
Although thousands of shells of these mollusks are washed 
ashore in all parts of the world, the animal is almost unknown, 
but three perfect individuals, and several others, more or less 
imperfect, having been collected. The U.S. Coast Survey Steamer 
Blake, in 1878, dredged a Spirula with its mollusk, in the West 
Indies, at the great depth of 950 fathoms. Prof. Owen’s last 
memoir on the Spirula adds materially to what was heretofore 
known respecting it. (Ann. Mag. Nat. Hist., 5 ser., iii, 1, 1879.) 
He shows that the mantle terminates posteriorly in two lateral 
flaps which cover the sides of the shell, leaving it partly exposed 
dorsally and ventrally. Posteriorly, between the lobes, is an 
elliptical, convex body, with a central depression or disk, flanked 
by a pair of oblong productions, perhaps homologous with fins, or 
at any rate resembling the small lateral-terminal fins of Zoligopsts. 
The terminal disk is, perhaps (as long ago described by Rum- 
phius), a true sucker, enabling the animal to attach the posterior 
end of its body to any object, leaving the arms free to exercise 
their prehensile power on passing objects of food. This wonderful 
terminal sucking organ is not found in any other cephalopods, 
but may have been possessed by the animal of Ammonites, 
supposing it to have been related to the Spirula rather than 
the Nautilus. The anatomy of Spirula, which is carefully worked 
out and illustrated in Prof. Owen’s memoir, shows it to belong 
to the dibranchiate decapod cuttle-fishes, as already indicated 
by previous studies. Whilst Spirula possesses natatory powers 
superior to the Nautilus, in the action of its webbed arms, addi- 
tional to that of the funnel, the former are so small in proportion 
to the size of the animal, and the fins are so rudimentary as to 
indicate sedentary habits. Prof. Owen observes that in Spirula, 
as in Nautilus, ‘“‘ the shell serves as the point d’appui of the 
retractors of the funnel and of the head with its locomotive and 
prehensile organs. Moreover, the last chamber of the shell in 
Spirula also receives part of the visceral mass, viz., the hind ter- 
mination of the liver, which, covered by its capsule, and this again 
by the peritoneum or a delicate aponeurosis continued from the 
attached shell-muscles, constitutes the hemispheric mass that 
fills the chamber and forms or sends off the beginning of the 
membranous siphon. . 
In another memoir, Prof. Owen shows that the dorsal portion 
of the animal of Spirula is placed towards the outer wall of the 
shell, which is the reverse of the relative positions of animal and 
shell in both Nautilus and Ammonites, showing that the spiral 
growth of the shell cone took a contrary direction. He agrees 
that the aptychi are developed on the spadix of Ammonites, and 
are true opercular bodies; consequently the Ammonite could 
