2 Jackson, On a Xe7v Carbo)iiferous Nautiloid. 



Since Mr. Crick furnished his description, I have discovered in the 

 Manchester Museum another example of the same species from the 

 Pendleside Series, Pule Hill, Marsden, which is in a more adult stage 

 of growth. This has necessitated the drawing up of a revised 

 description, as follows. 



Description of the Species. 



Calonautilus irapezoidalis, n. sp. 



Nautilus siibsuiaitus, G. Wild, Trans. Manch. Geol. Soc, vol. XXL, 

 1892, pi. II., fig. 5 ; pi. III., fig. 3 (not of Phillips). 



Sp. Char. — Shell of medium size, rapidly increasing, evolute, com- 

 posed of about three whorls, rather widely umbilicated, and with a large 

 central vacuity ; greatest width at the umbilical margin ; whorls only 

 just touching, inclusion nil ; umbilicus wide, with steep, step-like sides, 

 and a well defined sub-angular margin (umbilicolateral keel), which 

 becomes somewhat rounded at the fully-adult stage. Whorls trapezoidal 

 in transverse section, about one-fourth wider than high ; indentation 

 nil ; periphery flattened, well-defined, with a distinct raised, broad and 

 slightly concave, band down the centre, on each side of which there is 

 a narrow and rather shallow longitudinal sidcus, limited by the periphero- 

 lateral keel ; sides convergent, well defined both from periphery and 

 umbilical zones, their outer half feebly conAve, their inner half 

 moderately convex, a median longitudinal ridge being present in early 

 stages and passing away later (see remarks below) ; umbilical zone well 

 defined from the lateral area, almost at right-angles to the mesal plane 

 of the shell. Body-chamber probably about a volution ; aperture 

 trapezoidal in outline, about one-fourth wider than high ; peristome not 

 present, but, judging from the lines of growth, with a well-marked 

 sinus, on the inner half of lateral area, a prominent crest at the 

 periphero-lateral angle, and a deep hyponomic sinus occupying the 

 greater part of the peripheral area. Camerae not very deep; septa 

 feebly concave; where the whorl has a transverse diameter of 15 mm. 

 the sutures are 5 mm. apart, at 8 mm. diameter they are about 3 mm. 

 apart ; in the young shell they are somewhat variable ; sutures with 

 a moderately deep lobe extending across the lateral area and a shallow 

 lobe across the peripheral area (in the young stage this lobe is central). 

 Siphuncle close to the ventral surface. Test composed of two layers, 

 the internal very thick, the external extremely thin; surface ornamented 

 with very fine close-set stride, which are forwardly inclined and 

 sigmoidally curved on the sides, forwardly projected at the periphero- 

 lateral angle, and form a deep, broad, backwardly directed sinus upon 

 the periphery, corresponding with the emargination of the aperture ; 

 these transverse strire are seen (with a lens) to be crossed by extremely 

 fine regular longitudinal wavy lines on both the periphery and the sides, 

 especially at the periphero lateral keel ; along the middle of the lateral 

 area there are traces of several fine longitudinal ridges on a portion of 

 the largest example. 



