64 
NAUTILOIDEA. 
about as far from each other as the ridges are apart, and slightly 
extended transversely so as to form indistinct rows across the 
whorls, nearly direct on the sides, and with a slight backward wave 
on the periphery. Septa moderately concave, with nearly simple 
edges [sutures], having a slight backward wave on the prominent 
middle of the sides, nearly direct across the periphery. . . . This 
species seems to be liable to considerable variation in form from 
pressure, and especially a flattening of the sides, which, however, 
is certainly not the normal form. I have not seen the siphon, but 
Martin places it a little within the outer edge.” {M^Coy.) 
Remarhs. The dimensions of the type specimen (which is ex- 
quisitely preserved) are : greatest diameter 1 4 lines, breadth of the 
umbilicus 6 lines. The body-chamber is not known. The apical 
portion of the shell, which is beautifully preserved in Martin’s 
specimen, is obtusely pointed. M‘Coy observes that this species is 
not very uncommon in the black beds over the main Carboniferous 
Limestone of Derbyshire.” Gyroceras tessellatum, de Koninck 
{infra^ p. 67), is a very closely allied species, with similiar form and 
ornaments; hut the whorls are represented in de Koninck’s figure* 
as out of contact from the very commencement, which, if correct, 
would be sufficient to separate the two forms. 
Horizon. Carboniferous Limestone. 
Locality. Jfear Ashford, Derbyshire. 
Represented in the Collection by the type specimen figured and 
described by Martin {loc. cit.). 
Gyroceras Hibemicum, Foord. 
Char. Shell discoid, composed of two and a half to three 
whorls with a large central vacuity. The transverse section is sub- 
quadrangular, the convex side being depressed. The ornaments 
consist of numerous acute, longitudinal ridges, of which there are 
nine coarse ones upon the sides, and thirteen or fourteen very fine 
ones upon the periphery. The ridges are fine and somewhat indis- 
tinct at the lower part of the whorls, facing the umbilicus, and 
become gradually stronger, as well as more distant, till the edge of 
the periphery is reached, upon the surface of which they are ex- 
tremely delicate, especially towards the median line. Crossing the 
ridges are a series of very fine, discontinuous, transverse lines, 
about six in the space of ^ inch ; these form sharp nodes at their 
intersection with the ridgps, and give a beautiful cancellated 
Faune du Calc. Carb. de la Belgique, 1880, pt. ii. pi. xxxiii. ff. 6, 6 a. 
