imperfectly -defined Species of Jurassic Nautili. 271 



4. Nautilus robustus, sp. nov. 

 Fij?. 5. 



Nautilus robustus. — a, lateral view, showing the cast of part of the body- 

 chamber, the test being present in the septate part of the shell, where 

 a few lines of growth are indicated ; b, front view. Drawn from 

 a specimen in the British Museum (no. 37010). Rather less than one 

 third natural size. 



Sp. char. Shell of robust habit, slightly compressed on the 

 sides and flattened on the periphery, especially towards the 

 aperture ; the angles formed by the junction of the sides and 

 periphery rounded. Umbilicus open and exposing almost all 

 the inner whorls ; its sides rounded and rather steeply sloping. 

 Aperture wider than high. Septa 1 inch distant from each 

 other in the median line of the periphery, where the whorl 

 has a thickness of 3^ inches; in the middle of the sides their 

 distance is only half an inch ; the last two septa are only 

 three quarters of an inch apart on the periphery. The 

 siphuncle has not been seen. The body-chamber occupies at 

 least one half of the last whorl. The test is very thick and 

 its surface smooth, or marked only with lines of growth, as 

 seen in fig. 5, a. 



Remarks. There are three examples of this fine species in 

 the British Museum Collection, two of which are adult shells 

 and the other in the adolescent stage of growth. The largest 

 specimen (the figured one) measures about 8 inches in its 

 greatest diameter and about 5^ inches in its greatest width. 



This species is most nearly allied to Nautilus toarcensis. 



