464 



orbicular in its general form, but not sphseroidal, being con- 

 siderably depressed ; it is generally of a pale colour, and nearly 

 white, tliougli sometimes covered with a rusty epidermis; the 

 posterior part is covered with radiating, irregular, reddish-brown 

 stripes ; which continue to the centre, and are more numerous 

 and close-set on the dorsal part ; in front it is destitute of stripes. 

 The aperture is of an oblong heart-shape, and rather narrow, and 

 the umbilicus is completely covered. 



3. Nautilus ambiguus (pi. xcvii. f. 2), 7iohis. 



Testa suborbicularis, subventricosa, pallescens, postice ferru- 

 gineo radiatim multistrigata, strigis ad centrmn discontinuis, 

 supra dorsum paucioribus, subcontiguis ; apertura oblongo-cor- 

 data, lata ; umbilico clauso. 



This may possibly be only a variety of the foregoing ; there 

 are, however, several differences which appear to be constant. It 

 is nearly the same in general form, but not so much depressed, 

 its aperture is oblong- cordate, but wider than that of N. Ponqnlius : 

 it is usually nearly white, with reddish-brown radiating stripes, 

 wliich are rather close-set on the dorsal part, but do not continue 

 to the centre ; the umbilicus is entirely covered. 



3. Nautilus umbilicatus (pi. xcviii. f. 7), Lister, (not 

 Linn.) N. scrobiculatus, Solr. MS. Billwyn. Descr. Catal. p. 33. 



Testa suborbicularis, subdepressa, utrinque late umbilicata, 

 marginibus unibilicorum rotundato-angulatis ; lateribus subru- 

 gosis ; pallescens, postice radiatim ferrugineo strigata, strigis ad 

 dorsum contiguis, versus centrum discontinuis, umbihco ferru- 

 gineo, radiatim substrigato. 



This species is entitled to the name of umbilicatus, because that 

 name was given to it by Lister, and Linne's umbilicatus is not a 

 Nautilus, but one of the minute Foraminifera. We have, there- 

 fore, dropped Solander's manuscript name, afterwards published 

 by Dillwyn, of scrobiculatus. This is one of three umbilicated 

 species in which the outer edge of the umbilicus forms a rounded 

 angle ; the umbilicus is also larger than in the other species. The 

 streaks of colour, which are close-set on the dorsum, do not con- 

 tinue on the sides towards the umbilicus. 



4. Nautilus macromphalus (pi. xcviii. f. 4, 5), nobis. 



Testa suborbicularis, subventricosa, utrinque umbilicata, mar- 

 ginibus umbilicorum rotundatis ; pallescens, postice radiatim fer- 



