DESCKIPTION OF PLATES. 815 



a.i. Ala infundibuli in diastole. 



n.in. Nuchal membrane detached from the anfractus of the shell. 



e. Eye with the ophthalmic tentacles on either side of it. 



Fig. i. Dorsal view of young N. pompilius to show relations of hood, nuchal membrane 

 and mantle in the nuchal region. 



n.m. Nuchal membrane passing round on either side to coalesce with the alae infundibuli. 



b.w. Portion of body-wall between the base of the nuchal membrane and the line of 

 insertion of the dorsal lobe of the mantle. 



d.p.f. Dorsal lobe of mantle turned back. 



s.m. Shell-muscle. 



si. Siphuncle. 



Fig. 5. Dorsal view of cephalic region of a male specimen of N. macromphalus in which 

 the right anterior half of the hood had been apparently bitten away and the edges healed up. 



f. Funnel. 



in. Buccal cone. 



sp. Cyst of spermatophore, with the apices of some of the extrabuccal tentacles exposed 

 on either side. 



s. Spadix. 



Fig. 6. Similar view of another specimen in which a piece had been bitten out of the 

 hood so as to expose the entire cyst of the spermatophore (sp.), which is held by the two 

 dorsal tentacles of the extrabuccal series on each side. 



PLATE LXXVIII. 



Figg. 1 and 2. Two male iV. pompilius from below with mantle drawn back, showing 

 (in Fig. 2) situs inversus of the genital apparatus. These specimens are now in the Zoological 

 Museum of the University of Cambridge. 



v.n. Visceral nerves. 



os'. Submedian osphradia, separated by an interval in Fig. 1, coalescent in Fig. 2. 



n.s. Needhamian sac of the vas deferens. 



Fig. 3. Side view of cephalopodial region of N. umbilicatus to show the character of 

 the hood. 



a. Sulcate tentacle of spadix (10th tentacle of the extrabuccal series). 



b. Tessellate tentacle of spadix (11th of the series). 

 p.g. Preputial gland. 



e. Root of eye, which had been removed by means unknown to me ; a bristle is passed 

 into the olfactory labyrinth. 



f. Funnel 



a.i. Ala infundibuli. 



The digital tentacles of the left side have been cut away in order to expose the spadix. 

 Fig. 4. Cephalopodium of N. macromphalus with erected spadix. The hood has been 

 divided in the middle line. Specimen deposited in the Museum at Cambridge. 



g. Clans of spadix (9th tentacle of extrabuccal series), 

 sp. Cyst containing spermatophore. 



c.e. Cut edge of hood, 

 e. Eye. 



