nautilid-t:. 
169 
abruptly towards the umbilicus. The aperture is nearly perfect and 
presents a moderately deep ventral emargination. The section is 
much wider than high, the ratio of the ventro-dorsal to the trans- 
verse diameter, as nearly as can be computed, being as 40 : 25. The 
test is rather thick and is marked with numerous irregular lines of 
growth, traces of which are visible upon the pyritized inner layers 
of the shell, which also exhibit faint longitudinal lines and punc- 
tures, the latter apparently conforming to the direction of the lines 
of growth. Xothing is seen of the septa or siphuucle. 
The species nearest to this form is Solenoclieiliis Caledonicus^ but 
the latter expands more rapidly and there is no indication in the 
present form of the lateral spout-like projections in the aperture 
characteristic of S. Caledonicus. 
Horizon. Coal-Measures. 
Locality. Halifax, Yorkshire. 
Solenocheilus dorsalis, Phillips, sp. 
[See fig. 27, supra, p. 166.] 
1836. Nautilus dorsalis, Phillips, Geol. of Yorkshire, pt. ii. p. 231, 
?pl. xvii. f. 17, pi. xviii. ff. 1, 2. 
1843. Nautilus dorsalis, Portlock, Geol. of Londonderry, p. 405. 
1844. Nautilus dorsalis (pars), M‘Coy, Synop. Carboniferous Foss. Ire- 
land, p. 23 (var. y of Phillips). 
1849. Cryptoceras dorsalis, d’Orbignv, Prodr. de Paleont. Stratigr. 
vol. i. p. 114. 
1854. Nautilus dorsalis, Moms, Cat. of British Fossils, 2nd ed. p. 308. 
1875. Nautilus dorsalis, Baily, Characteristic British Fossils, p. 117, 
pi. xl. f. 7. 
1876. Nautilus dorsalis, Armstrong, Young, and Robertson, Cat. of 
Western Scottish Fossils, p. 59. 
1883. Asymptoceras dorsale, Hyatt, Proc. Boston Soc. Nat. Hist. 
vo1. xxii. p. 297 (footnote). 
1878. Nmdilus dorsalis (pars), de Koninck, Faune du Calcaire 
Carbonifere de la Belgique (Annales du Mus. Roy. d’Hist. Nat. 
de Belgique, tom. ii.), p. Ill, pi. xviii. ff. 1 «, 1 b, 2, 3 (? var. y of 
Phillips).] 
Sp. Char. Shell Nautilus-like, tumid, consisting of about two 
rapidly enlarging, very involute whorls. Umbilicus very small, 
though exhibiting the inner whorls ; there is a small central per- 
foration. 
The septa are wide apart, being about 6 lines distant from 
each other, where the transverse diameter is 15 lines (type speci- 
men). The siphuncle is close to the peripheral margin. The 
