NVrXILID^. 
87 
phery. Surface ornamented with transverse lines of growth ; the 
young having also fine longitudinal ridges which become obsolete 
in the adult h Some species (JS^autilus sidcatus^ J. Sowerhy, e.g.) 
are furnished with a number of revolving sulci. 
Type, Nautilus {Discites) cUscors, AI‘Coy^ Carboniferous. 
Remarl-s. As the first species described by M‘Coy — D. costellatus 
— which would naturally have been taken as the type of Discites, 
disagrees with his definition of the genus, the second in order of 
description has been selected, viz. Discites discors, M‘Coy. 
Hyatt ^ has taken D. costellutus as the type species, stating that 
it was apparently the young of a species similar to D. discors, 
H‘Coy. This opinion is, however, contradicted by the evidence of 
the specimens in the British Museum, which clearly show that the 
young of Discites did not resemble D. costellatus in the slightest 
degree. The latter is strongly ridged and has a broadly rounded 
periphery, the whorls being in section much wider than high, which 
is exactly the reverse of what is the case in D. discors. The longi- 
tudinal ornaments in the young of the latter are, moreover, very 
much finer than in D. costellatus, and in fact are best described as 
“ fine thread-like lines,” to which the term “ costellate ” would 
certainly be very inappropriate. 
Professor Hyatt ^ has proposed the name Discitoceras in lieu of 
Discites, on the ground that the latter has been used by AYalch and 
Schlotheim for other molluscan genera ; but as it has not been re- 
tained for the types to which those authors applied it, there can be 
no reason why it should not be employed for the section founded 
by M‘Coy, which has now become so familiar to pala)ontologists. 
Discites Omalianus, de Koninck, sp. 
183G. Nautilus tetragonus, Phillips, Geol. of Yorkshire, pt. ii. p. 233, 
pi, xvii. f. 24, pi. xxii. ff, 33, 34. 
1851. Nautilus Omalianus, de Koninck, Descrip, des Anim. Foss, du 
Terr. Garb, de la Belgique, Supplem. pp. Gl, 711 (doubly paged), 
pi. lx. ff. 3, a-d. 
1854. Nautilus {Discites) tetragonus, Morris, Cat. British Foss. 2nd ed. 
p. .309. 
Sp. Clmr. Shell discoid, bluntly pointed at the apex, somewhat 
compressed laterally ; composed of about three volutions, all ex- 
^ The shell is never “ nodiferous ” in this group, as Meek has described it. 
^ Synop. of the Carboniferous Foss. Ireland, 1844, p. 17. 
^ Proe. Boston Soc. Nat. Hist. 1883, vol. xxii. p. 292. 
' Ibid. 
