70 PAUNA OP BALTTOHISTlN. 



"but the broad and comparatively low, widely overlapping whorls are well represent- 

 ed. I consider the chief characteristic features of Nautilus sublcevigafua to be its 

 globose shell, low, rounded, deeply overlapping whorls, and the sudden lateral expan- 

 sion of the shell towards the end of the body chamber. These features will readily 

 distinguish this species from Nautilus subfieuriamianus, d'Arch.,to which it is other- 

 wise closely related. It is, however, almost certain that the species here described is 

 identical with Nautilus Icevigatus, d'Orbigny, which shows the same characters of the 

 shell, the globose shape, small umbilicus, and expansion of the end of the body cham- 

 ber. The only difference seems to exist in the position of the siphuncle, which is cer- 

 tainly nearer to the dorsal side in the Nautilus labechi than in Nautilus- Icevigatus, 

 This may perhaps be accidental, and I am by no means convinced that this would 

 affect the specific identity of the two forms, particularly as Stoliczka has described 

 under the name of Nautilus sublcevigatus, d'Orbigny, a form from Southern 

 India which is unquestionably identical with Nautilus labechi, as I discovered by 

 comparison of Stoliczka's original, pi. V, fig. 3, with those from the Bind and 

 Baluchistdn specimens. Stoliczka has so ably discussed the differences between 

 Nautilus bouchardianus, d'Orb., Nautilus sphcericus, 'Foxhes, and Nautilus sub- 

 lcevigatus, d'Orb., that I need not dwell at length on this subject. 



Another form closely related, if not identical, is Nautilus charpentieri, Leym.,i 

 but I refrain from expressing a definite opinion without having a specimen of this 

 species for comparison. 



Nautilus suBFiETJRiAirsiANTJS, d'Archiac and Haime. PI. XX, fig. 3-3a ; 



PI. XXI, fig. l-la. 



1854. Nautilus swbfleuriausianug, d'Archiac and Haime, Descr. des Anim. foss. des Groupe Numm. de I'lnde, 



page 337, pi. XXXV, fig. 1, a. 



Diameter of the shell 120 mm. 



Diameter of the umbilicus 8 „ 



Height of the last whorl from the umbilical suture 67 „ 



Height of the last whorl from the preceding whorl S9 „ 



Thickness of the last whorl . . ^ 65 „ 



Approximate number of septal to one volntion . , 40 



The discoid shell is laterally compressed ; at an early age, when the diameter of 

 the shell was not more than 6 mm., the shell was apparently perfectly globose, the 

 thickness of the whorls greatly exceeding their height ; with advancing age the 

 height increases more quickly than the thickness, and the proportion of height to 

 thickness, which in early stages is 4 : 8, changes later on to 22 : 39 ; thus in adult 

 specimens the height exceeds the thickness of the whorls. At the same time the 

 whorls overlap each other so completely that only a very narrow umbilicus remains, 

 which was probably filled by a callosity. The cross section of the whorls is there- 

 fore transversely elliptical in younger, sagittate in adult specimens. 



The shell attains its greatest thickness at the umbilical edge, and from there 

 the somewhat flattened sides slope towards the rounded ventral side. 



' MIm. de la Soo. G^ol. de Prance, 2nd Ser., Vol. IV, p. 198, pi. C, fig. 2. 



