31 



CEfCK : SPECIES OF NAUTILUS FROM THE IJJFEEIOR OOLITE. 121 



hyponomic sirnis. Chambers rather shallow, eleven or twelve in the 

 last half whorl of the septate portion ; septa feebly concave ; suture- 

 line with a simple shallow curve on the side, and a broad, very shallow 

 sinus on the periphery. Position of the siphuncle unknown. Test 

 almost smooth, with very faint growth-lines, which are slightly 

 waved and nearly direct on the sides, but form on the periphery a deep 

 broad sinus corresponding to the hyponomic sinus of the aperture. 

 Dimensions. 



Diameter ... ... ... 81 mm. 



Height of outer whorl ... 53 ,, 



Height of outer whorl above 

 preceding whorl 



Thickness ... ... ... 62-5 ,, (near the periphery). 



Width of periphery ... about 43 ,, 



At a diameter of 70 mm., i.e. at about one-third of the depth of the 

 body-chamber, the dimensions of the same specimen are : 



Diameter ... ... ... 70 mm. 



Height of outer whorl ... 40 ,, 



Thickness ... ... ... 48 ,, (near the umbilicus). 



Width of periphery ... ... 34 ,, 



Remarlcs. — At the aperture the shell is thickest near the periphery, 

 but elsewhere its greatest thickness is close to the umbilicus. 



This species is represented in the British Museum Collection by the 

 example (IS^o. C. 3187), the dimensions of which are given above; this 

 is probably an adult shell, the last two septa being much closer together 

 than the rest. On the internal cast of the body-chamber the impression 

 of the anterior border of the shell-muscle a,nd of the annulus is pre- 

 served as an incised line, which forms a bold broad orad-convex curve 

 on the greater part of the lateral area, being in the centre of this area 

 about 27 '5 mm. in advance of the last suture line, and a very shallow 

 orad-concave curve on the periphery, where it is only about 3 mm. 

 from the last suture-line. The peripheral portion of the peristome 

 with its deep hyponomic sinus is well preserved. 



This is evidently the species figured by E. Eudes-Deslongchamps 

 as Nautilus ohstructus (Jura Normand, Monog. vi, pi. xi, figs. \a-d, 

 2ar-c, 1878). Unfortunately,, owing to the death of the author, no 

 description was published, but the figures are so good that the species 

 can be readily identified. 



It may be mentioned that in the explanation of the plate, 

 Deslongchamps describes the specimen represented in figs. 2a-o as 

 a " variete legerement comprimee, peutetre femelle," from which 

 it would appear that he regarded the more inflated shell as the male, 

 and the more compressed as the female. This agrees with the most 

 recent observations on the subject. 



The British example agrees with the specimen which it would seem 

 that Deslongchamps regarded as the male (figs. 1 a-d). 



Affinities and Diffierences. — This species differs by its less inflated 

 lateral area and its closed umbilicus from N. lineolatus, Foord & Crick. 



