118 NAUTILUS. 



parent, flattish, convex on the upper-side, concave and 

 deeply perforated underneath, with a slight keel-like ridge : 

 spires four, bordered on the outside with a whitish opake; 

 stripe running spirally to the centre : on the first volution 

 are three compartments, nearly at equal distances from 

 each other, the lines of junction appearing like white 

 curved stripes radiating from the centre, the first of them 

 placed distant from the aperture, which is narrow, some- 

 what heart-shaped, and clasping the spire on both sides : 

 diameter hardly a quarter of an inch. 

 On aquatic plants, v. v. 



3. Nautilus rotatus. Star Nautilus. 



Nautilus Calcar. Montagu, pi. 15. f. 4 ff'alker, f. 66. 



Shell smooth, equally convex on both sides, rather more 

 raised in the middle, with a strong ridge on the back, which 

 is entire : joints six, marked by elevated flexuous lines ra- 

 diating from the centre like a star, but not quite reaching 

 to the outer margin : aperture half heart-shaped, clasping 

 the body equally on both sides, furnished with a small per- 

 foration : minute. 



On shells, corallines, and other substances, v. v. 



4. Nautilus laevigatulus. Smooth Nautilus. 



Montagu, pi. 18. f. 7, Walker, f. 67. 



Shell smooth, opake, pale rusty-brown, considerably and 

 equally convex on both sides, declining to a rounded mar- 

 gined edge, but not perfectly forming a keel-like ridge : 

 joints about ten, marked by flexuous rather raised lines, 

 which emanate from the margin and are rather of a deeper 

 color : aperture surrounded by a rim, forming a triangle, 

 and not attached to the body : minute. 



In fine and drifted sand. v. m. 



5. Nautilus depressulus. Depressed Nautilus. 



Montagu, pi. 18. f. 9 Walker, f. 68. 



Shell glossy- white, semitransparent, flat, equal on both 

 sides and without any prominent ridge : joints about nine, 

 marked by opake curved lines radiating from the centre, 

 where there is a small transparent spot, and the curved 



lines 



