ACTINOCEEATID^. 
189 
1880. Orthoceros giganteum, de Koninck, Faiine dii Calc. Carbonifere 
de la Belgique, tom. y. p. 75, pi. xliv. if. 5-10. 
1835. Orthoceratites giganteus, Kutorga, Beitrag zur Geognosie 
und False ontologie Dorpat’s, p. 32, Taf. yi. f. 6.] 
Sp. Char. Shell yery large; straight. Section nearly circular. 
Rate of increase from 1 in 7 to 1 in 5. Septa moderately convex, 
increasing somewhat rapidly in their distance apart ; for example, 
in a specimen measuring 2 feet 10 inches in length, the septa are 
only 1 line distant at the smaller extremity, while at the larger the 
interval between them has increased to 1 inch. In a large fragment 
consisting of the greater portion of the body-chamber, with two 
septa attached, the latter are distant 1| inch, the diameter being 
here about 7 inches. The siphuncle is not large in proportion to 
the dimensions of the shell ; it is a little eccentric in the young, 
e. less than its own diameter from the centre, tending to become 
more nearly central in the adult shell ; it is much inflated between 
the septa into depressed spheroidal segments twice as wide as long. 
The outer surface of the test is generally wanting, and the inner 
Inycr being quite smooth has led authors to describe the species as 
having a perfectly smooth shell ; but there is a specimen in the 
Collection which has a distinctly striated surface, above the smooth 
layer, the ornaments consisting of fine transverse lines, of which 
there are about three in the space of a line 
liemarlcs. This shell in its great size and robustness of habit 
surpasses all others of its kind in the British rocks. M‘Coy, in 
chronicling its occurrence in the red limestone of Castle Espie 
Comber, in Ireland, observes that it sometimes attains a length of 
feur feet, imperfect at both ends ” (‘ Carbonif. Foss, of Ireland,’ 
p. 11) ; and Sowerby (Min. Conch.) computes its length as some- 
times exceeding 8 feet. A huge fragment, the whole of which 
appears to be septate, measures 2 feet 5 inches in length, the 
diameter of the larger extremity being about 8 inches, that of the 
smaller about 4| inches. 
Horizoyi. Carboniferous Limestone. Calciferous Sandstone (Close- 
burn ; Carluke District). 
Localities. British. Boliand, Yorkshire ; near Caldbeck, Cumber- 
land; Yewbery, Derbyshire; Closeburn, Dumfriesshire; Carluke 
District ; Ireland. — Foreign. Vise', Belgium. 
Represented by a magnificent series of specimens, containing the 
^ The specimen showing these markings is registered C 325 in the Collection, 
but without a locality. It is, however, without doubt British. 
