464 



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

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

 white, though 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 umbdicus is completely covered. 



2. Nautilus ambiguus (pi. xcvii. f. 2), nobis. 



Testa suborbicularis, subventricosa, pallescens, postice ferru- 

 gineo radiathn multistrigata, strigis ad centrum discontinuis, 

 supra dorsum paucioribus, subcontiguis ; apertura oblongo-cor- 

 data, lata ; umbilico clauso. 



Tins 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. Pomjrilius : 

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

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

 to the centre ; the umbdicus is entirely covered. 



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

 Linn.) N. scrobiculatus, Solr. MS. Dillwj/n. Descr. Catal. p. 33. 



Testa suborbicularis, subdepressa, utrinque late umbilicata, 

 marginibus umbilicorum rotundato-angulatis ; lateribus subru- 

 gosis ; pallescens, postice radiatim ferrugineo strigata, strigis ad 

 dorsum contiguis, versus centrum discontinuis, umbilico ferru- 

 gineo, radiatim substrigato. 



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

 name was given to it by Lister, and Linrie'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 umbdicata, mar- 

 ginibus umbilicorum rotundatis; pallescens, postice radiatim fer- 



