288 PROCEKDINGS OF THE JIALACOLOGICAL SOCIETi'. 



Since Dr, Foord's original description of Nautilus mokattamensis 

 appeared, the National Museum has received as a donation from 

 H. Pearson, Esq., a so much better example of this species from the 

 Mokattam escarpment, near Cairo, that it seems to merit description. 



This specimen' (PI. VIII, Figs, a, i), altliougli smaller than either 

 of the other examples in the collection, is a fairly complete internal cast 

 of tlie septate portion of a shell, having the following measurements : 

 diameter, 79 mm. (1) ; height of outer whorl, 45 ram. (0-569) ; ditto 

 above preceding whorl, 29 mm. (0-367) ; greatest thickness, 62 mm. 

 (0*784); width of umbilicus, 6 mm. (0*0759). The last two septa are 

 17'5mm. apart at the centre of the periphery. Where the wliorl is 

 only 16 mm. liigh and its height above the preceding whorl 10'5 ram., 

 the siphimcle is very near the dorsal (inner) edge of the septum, but 

 with the growth of the shell the siph uncle gradually recedes from the 

 dorsum iiutil at the anterior end of tlie speciraen, i.e., where the whorl 

 is 45 mm. high, it becomes almost exactly median. Commencing 

 suddenly near the median line of the peripheral area of the end of the 

 penultimate whorl, and extending thence over the first sixth of the 

 outer whorl, there is, a little on one side of the median line, a longi- 

 tudinal fairly deep and broad groove ; this ceases rather abrnptly, 

 and almost exactly on the median line of the periphery another narrow 

 groove originates and extends over about another sixth of tlie outer 

 whorl, broadening in its course and gradually disappearing; the median 

 line of the peripheral area of the rest of the whorl is occupied by 

 a fairly distinct raised line (the ' normal line '). The longitudinal 

 groove is accompanied on each side by several obscure irregularly- 

 spaced coarse backwardly-curved ribs, and is evidently the result of 

 injury to the shell. The greatest thickness of the whorl is at 

 about two-fifths of the height of the whorl from the edge of the 

 umbilicus. No portion of the test is present; if it had been 

 preserved the umbilicus would doubtless have been very small, or 

 possibly even closed. The septa are moderately concave, and their 

 dorsal margin is projected forward ; there is no dorsal (annular or 

 coluraellar) lobe even where the whorl is only 16 rara. high, and its 

 lieight above the preceding wliorl 10*5 mm . 



The description of the species may therefore be emended as 

 •follows : Shell (cast) of medium size, ovate, moderately inflated, 

 rather rapidly expanding; greatest thickness at about two-fifths of 

 the height of the outer whorl from the edge of the umbilicus, about 

 four-fifths of the diameter of the shell ; height of outer whorl about 

 four-sevenths of the diameter of the shell. Whorls (? number) ; 

 inclusion alraost complete ; umbilicus small. Whorl semi-elliptical 

 in transverse section, about one-third wider than high ; indented to 

 about one-third of its lieight by the preceding whorl; periphery not 

 very broadly rounded, imperfectly defined from the sides, exhibiting 

 ' norraal line' ; sides convergent, flattened, feebly convex ; urabilical 

 zone sloping towards the centre of the urabilicus, convex, with 

 subangular margin. Length of body-chamber and aperture not seen. 



' British Museum Collection, Geol. Dept., register No. C. 12426. 



