117 



DESCRIPTIONS OF NEW OR IMPERFECTLY KNOWN SPECIES OF 

 NAUTILUS FROM THE INFERIOR OOLITE, PRESERVED IN 

 THE BRITISH MUSEUM (NATURAL HISTORY). 



By G. C. Ckick, F.G.S., etc., 

 Of the British Museum (Natural History). 



Read IZth May, 1898. 



Sexual dimorphism has for a long time been recognized among the 

 shells of the recent Kautilus, and it is interesting to find the same 

 character exhibited by species which occur in a fossil state. In the 

 recent Nautilus the body-chamber of the shell of the male is more 

 inflated than that of the female, particularly at the sides, and hence 

 the aperture of the former is wider and more obtuse than that of the 

 latter. In the male the aperture of the shell is broad and more or 

 less elliptical ; in the female it is more or less oval, being some- 

 what compressed laterally, especially near the periphery. Similar 

 differences in the form of the body-chamber and of the aperture are 

 exhibited by the examples of some of the species described in the 

 present paper; they are therefore attributed to sexual dimorphism, 

 the forms having the relatively broader aperture being regarded as 

 the males, and those with a narrower and more elongated aperture 

 the females. 



Moreover, in some specimens it has been possible to trace very 

 clearly the position of the anterior boundary of the muscular attach- 

 ment. In the shell of a recent JSTautilus this boundary exists as 

 a slightly raised line on the inside of the body-chamber, and hence 

 on the internal cast of the body-chamber, such as would be preserved 

 in a fossilized state, this boundary appears as a finely incised line. 



1. Nautilus BRADroRDEisrsis, n.sp. Figs. I & II. 



Tyji^es.— British Museum Coll., Nos. C. 3177 and C. 4503. 



bpecific Characters. — Shell rather small, compressed, rapidly 

 increasing; greatest thickness in the adult at about the middle 

 of the lateral area, about three - fifths of the diameter of the 

 shell ; in the young nearer the umbilicus ; height of outer 

 whorl about three - fifths of the diameter of the shell. Whorls 

 two and three-quarters ; inclusion complete ; umbilicus closed by 

 a shelly callus, slightly depressed. Whorl oval in section, nearly 

 as wide as high ; indented to about three-tenths of its height by the 

 preceding whorl; periphery rather broad, somewhat convex (in the 

 less inflated form), sometimes slightly concave (in the more inflated 

 form); sides of the body- chamber inflated, but more flattened in 

 the septate part of the shell, gradually passing into the umbilical 



