HIND : NEW CARBONIFEROUS NAUTILOIDS. 
103 
Umbilicus large, exposing all the whorls. Whorl lunate in 
section, much wider than high, lower border convex ; periphery 
broad, gently concave, the margin acuteh^ angular, sides very 
gently convex. 
The septa are very numerous and deeply concave. The 
sutures have a deep backward curve on the periphery and also on 
the sides. Test was thin and marked by fine parallel striae. 
In the nepionic and neanic stages the test is ornamented by 
longitudinal lines. Apparently in the nepionic stage the whorl is 
free. The fragment is 95 mm. in diameter, and the breadth of 
the periphery 50 mm. 
Affinities. — A. Mutabile, M'Coy (Synopsis, Carb. foss. Ireland, 
p. 18, PI. iii., fig. 7), and A. Hibernicum, Foord and Crick (Geol. 
Mag., Dec. iii., Vol. x., p. 251, woodcut, p. 254) are much too 
discoidal and compressed to be mistaken for A. latum, A. trochlea, 
M'Coy (Synopsis, Carb. foss. Ireland, p. 19, PI. iii. fig. 4), of which 
only fragments are known, while larger than either of these species, 
has its whorl much higher and not nearly so broad as A. latum. 
It is probable that A. trochlea comes from a lower life zone than 
any of the other species of the genus, fragments having been 
obtained at Kendal, probably from Seminula beds and also from 
Tyrone. On the other hand, A. mutabile, A. hibernicum, and 
A. latum have all been obtained from upper Dibunophyllum beds. 
De Koninck, however, figures a fragment of A. trochlea from Vise. 
A. difficile, De Koninck (Faune, Calcaire, Carbonifere, 
Belgique, 1878, Pt. 1, p. 118), and A. discoideum, De Koninck, sp. 
(op. supra cit., PI. 33), have a closer aflSnity to A. mutabile than 
to the species now under discussion. 
The cephalopod fauna associated with A. latum in the 4 Laws 
Limestone contains the following species : — 
Stroboceras bisulcatum, De Koninck, sp. 
Coelonautilus derbiense, Foord. 
C. planotergatum, M'Coy, sp. 
C. cariniferus, Sow., sp. 
Coloceras coyanum, D'Orbigny, sp. 
Solenocheilus dorsalis, Phillips, sp. 
Actinoceras breynii, Martin, sp. 
Actinoceras giganteum, Sow., sp. 
