﻿BEITISH FOSSIL CEPHALOPODA. 109 



litic Mudstones of Skelgill ; by Salter, in Jukes's ' S. Staffordshire Coalfields/ from 

 Lower Ludlow, Parke's Hall, also Upper Ludlow, Coalbrookdale ; by Sollas, from the 

 Upper Llandovery, Wenlock, and Ludlow Beds of Pen-y-lan, Cardiff; by Baily, 

 from Cloonnamera, Bleaubeg, Derrymore Glen, and Fairy Mount ; and in the 

 Catalogue of Western Scottish Fossils, from Penwhapple Glen. Being originally 

 found in Sweden, we are not surprised that it ranges beyond there into Russia. 

 Species under the same name are recorded from Wisconsin and Illinois. 



Orthoceras coralliforme, M'Coy, PI. VII. fig. 6. 



1846. Orthoceras coralliforme, M'Coy, 'Synopsis of Silur. Foss. of Ireland,' pi. 1, fig. 3, p. 8. 



Type. — Section very slightly oval, the rate of increase 1 in 6, but rather irregular. 

 The ornaments are 30 longitudinal ribs, about one line apart, between which is an 

 intermediate one, and sometimes two or three, still finer, on each side of this. There 

 are also transverse riblets 4 or 5 per line. The septa are a little oblique, as indicated 

 by broken shelly plates outstanding from an external cast, called lamellae by M'Coy, 

 about \ the diameter apart. No siphuncle is seen in this example. Length, 3^- inches ; 

 diameter, § inch. From Lower Silurian, Tullyconnor, Leenane. In the Museum of 

 Royal Dublin Society. 



General Description. — The section is not very far from circular, and the rate of 

 increase is 1 in 6. No body-chamber nor aperture has been seen. The ornaments 

 are admirably shown on an external cast from Piedmont Glen. They are about 20 

 in the circumference in this, but 32 in others. To the cast these give a polygonal 

 appearance, but they are themselves acute and non-separate ; between each pair is 

 another, finer one. The surface is then beautifully cancellated, first, by sharp longi- 

 tudinal lamellae, 4 or 8 in number in each semi-interval, according as finer ones are 

 developed or not; these are rather irregularly spaced, on the average 10 per line : 

 secondly, by very regular transverse upward imbrications at an equal distance. The 

 septa are indicated at from \ to \ the diameter apart ; they are a little oblique and 

 but slightly convex. The siphuncle is f the diameter from the side, and is some- 

 what bulbous, the bulbs being cylindrical. The greatest diameter seen is If inches. 

 It will be seen that I take the " lamellas " of M'Coy for indications of septa ; they 

 are certainly not external ornaments, but internal projections due to the septa 

 breaking off. 



Relations. — The general character of the ornaments is similar to that of 

 0. Bacchus, but there are well-marked transverse imbrications, and the ribs are 

 more acute. When the ornaments are worn, it is difficult to separate this from 

 0. angulation, but they are quite distinct when well preserved. It may be considered 

 as the representative of the latter in the Lower Silurian rocks. 



