CEICK : SPECIES OF NAUTILUS EKOM THE IlSTFERIOIl OOLITE. 133 



by the preceding whorl; periphery broadly convex, somewhat 

 flattened, especially at the body-chamber ; sides inflated and passing 

 imperceptibly into the inner area; inner area convex, imperfectly 

 defined. Body-chamber occupying about one-third of the last whorl ; 

 aperture with a deep and broad hyponomic sinus. Chambers rather 

 deep, about eight in the last half whorl of the septate portion; 

 septa feebly concave ; suture-line with a simple shallow sinus on 

 the lateral area, and only a very shallow sinus on the periphery. 

 Siphuncle infra-central. Test 1 mm. thick, almost smooth, with 

 faint lines of growth, which curve backward on the outer portion 

 of the lateral area and form a deep wide sinus on the periphery. 

 Dimensions. 



(i) (ii) 



Diameter of shell ... ... 98 mm. 110mm. 



Height of outer whorl ... 59 ,, 62 ,, 



Height of outer whorl above ) or 41 



preceding whorl ) " " 



Thickness about 72f „ 84f ,, 



"Width of umbilicus ... ... 4 ,, 4 ,, 



(t Not including the test.) 



Remarhs. — To this species we refer two specimens in the British 

 Museum Collection — JN'os. C. 3181 (i) and C. 4496 (ii) ; their 

 dimensions are given above. In the example No. C. 4496 the last 

 loculus is much smaller than the rest, being only 7 mm. in depth at 

 the centre of the periphery, the adjacent one being 16 mm. deep. 

 Probably, therefore, this is an adult specimen. In both examples the 

 greatest width of the aperture is near the middle of the lateral area ; 

 the height of the aperture in proportion to its width is, however, 

 greater in (ii) than in (i), and the periphery of the former is less 

 depressed than that of the latter, but these differences are so very 

 slight that they may be only individual variations. 



There is also in the British Museum Collection another specimen 

 (No. C. 4489) which for the present at least we would refer to this 

 species. Its dimensions are as follows: — Diameter of shell, 93mra. ; 

 height of outer whorl, 53*5 ram. ; ditto above preceding whorl, 

 35mm.; greatest thickness, 70 mm. (not including the test); width 

 of umbilicus, 5 mm. It differs from the others in having a more 

 quadrate and more expanded aperture, and a somewhat larger 

 umbilicus. In this specimen the position of the anterior border of 

 the shell-muscle and of the annulus is clearly indicated on the natural 

 internal cast of the body-chamber by an incised line, which forms 

 a bold anteriorly convex curve on the lateral area ; in the centre of 

 the periphery this Hue is only 5 mm. in advance of the edge of the 

 last septum, but on the lateral area the most convex portion is as 

 much as 32 mm. in advance of the corresponding part of the same 

 septum. 



Affinities and Differences. — Compared with Nautilus siihrotiindus,^ 



1 Vide infra, p. 134. 



