(iliSEliVATlONS OK SPIKULA. 
1. External Conformation and Teguments. 
The body of is elongated, cylindrical, truncated posteriorly. The posterior 
extremity is constituted b)’ a “ terminal disk,” which is less distinct in Spirula 2 '>c^ronii 
(El. I. Hgs. 1-4) than in Spirilla australis (PI. II. figs. 1-3) and in Sp>irula reticulata 
(Figs. C, .1, and N in the text) ; it carries two small fins, parallel to the median sagittal 
plane, between which is an orifice leading into a little fossa. In the posterior half 
then.' are, botli dorsally and ventrally, two antero-posterior oval openings through which 
the Ia.st whorl of the shell very slightl}?^ projects. This “ body ” corresponds to the 
visceral sac, covered by the mantle, of Nautilus and of the Gastropods (“ episoma,” 
Huxley) ; the ccphalo-j)cdal mass (“ prosoma” or cephalopodium, Huxley) is united to the 
body by the “ mesosoma” (Huxley), that is to say, b}^ the nuchal region and the funnel, 
the latter (cjdpodium) belonging morphologically to the foot. 
'I'hcse dirtcrent j)arts : head, foot (arms), funnel, mantle, &c., must be separately 
examined. 
1. Head. — In the Challenger specimen this part was retracted into the pallial 
cavity (1*1. I. figs. 1, 2, 3) and a little distorted (PI. I. figs. 5, 6). The “ Blake” specimen 
(PI. II. fig. 1) had also the head slightly twi.sted. This asymmetry is not normal, however, 
ami has not been observed in other specimens ; Mt is a})parently a deformation due to con- 
traction. The heiul in its general conformation, like that of other Decapods, is characterised 
(in the Challenger and “ Blake ” specimens) by its rather considerable width, especially in 
the |)o8tcrior part ; it is more develojicd laterally than dor.so-ventrally. The eyes are 
placed laterally, .and behind them, but more ventrally, arc found the olfactory organs 
(ftco further on for the conformation of these organs). 
‘2. Arms. — As in all the Dcaijtods, there are, eight sessile arms, which arc in Spii'ula 
rather short, and two long pedunculated or tcnt.acular arms. 
n. SrAsile Amis. — The eight short arms arc i>crccptibly equal in length (PI. I. figs. 
I -3) ; their al>oral or external surface is rounded, except that there is a median longitudinal 
ri»Ig« . 'I’he internal face is flattened so a.s to form a surface for the acctabula, extending 
fn»ni the base U» the summit of each arm ; this surface is broad and bounded by a curved 
contour at the basal extremity and narrows gr.adu.ally towards the summit. The bases 
• Kor example, the individual studied by Owen in 1870. 
