130 PROCEEDINGS OF THE MALA.COLOGICAL SOCIETY. 



width, with convex margin, and convex and overhanging sides. Whorl 

 oval in section, the peripheral portion being the narrower ; periphery 

 broadly rounded, passing imperceptibly into the sides ; sides convex, 

 very slightly flattened ; inner margin convex, not sharply marked off 

 from the side, and overhanging the umbilicus. Length of body-chamber 

 not seen. Chambers rather shallow, their depth at the periphery about 

 two-fifths of the corresponding height of the whorl ; septa slightly 

 concave, suture-line with a broad and not very deep sinus on the 

 lateral area. Siphuncle near the periphery. Test — on the lateral area 

 nearly smooth, only with backwardly directed lines of growth ; on 

 the periphery with rather coarse longitudinal waved lines, which with 

 age encroach somewhat on the lateral area, with much finer lines in 

 the interspaces, the transverse lines of growth forming here a deep 

 broad hyponomic sinus. 

 Dimensions. 



Diameter ... ... ... ... ... 125 mm. 



Height of outer whorl ... ... ... ... 77 , , 



Height of outer whorl above preceding whorl ... 57 ,, 

 Thickness ... ... ... ... ... 65 ,, 



"Width of umbilicus ... ... ... ... 10-5 ,, 



Remarhs. — There is only one example of this species. It came from 

 Bradford Abbas, and Mr. S. S. Buckman, from an examination of the 

 matrix, considers it to have come from the " concavus-zone (probably 

 ITi/perlioceras-hed),^' a somewhat lower horizon than that containing 

 the i\^. suisinuatus, but the same as that yielding JV. crassisinuatus. 



The name of the species is derived from the overhanging character 

 of the inner portion of the whorl. 



Affinities and Differences. — Its less sinuous suture-line at once 

 separates this species from both N. suisinuatus, D'Orb. {N. sinuatus, 

 J. Sowerby), and iV. crassisinuatus ; whilst the form of its umbilicus 

 and the smoothness of the lateral area of the test distinguish it from 

 N. ornatus. 



Form, and Loc. — Inferior Oolite (" concavus-zone : probably Ilyper- 

 lioceras-'hed.^^ — S. S. Buckman) : Bradford Abbas, Dorset. 



7. Nautilus exteeebratus, n.sp. Fig. X. 



Tijpes.— British Museum Coll., Is^os. C. 3245 and C. 4498. 



Specific Characters. — Shell inflated, rather rapidly increasing ; 

 greatest thickness sometimes (i.e. in the less inflated form) close to 

 the edge of the umbilicus, sometimes (i.e. in the more inflated form) 

 at a short distance from the edge of the umbilicus, about three-fourths 

 of the diameter of the shell ; height of outer whorl rather more than 

 one-half of the diameter of the shell. Whorls fcAV ; inclusion nearly 

 complete ; umbilicus deep, about one-eighth or one-ninth of the 

 diameter of the shell in width, with steep sides and subangular 

 margin. Whorl subquadrate in section, its height about two- 

 thirds of the width ; indented to about three-eighths of its height 

 by the preceding whorl ; periphery broad, sometimes (i.e. in the less 



