﻿BEITISH FOSSIL CEPHALOPODA. 185 



unable to say whether any more characteristic specimens exist, and am obliged to 

 leave the species as a doubtfully British one. 



Distribution. — The species is said to come from the Lower Bala Beds of Knock- 

 dollian, Ayrshire. There is also a specimen in the Museum of Practical Geology 

 from the Durness Limestone, apparently the one figured in 'Siluria,' Fossil group 27, 

 fig. 5, as Oncoceras, whose peculiarities as shown in that figure are due entirely to 

 preservation, but which by the closeness of its septa might belong to the present 

 species. 



Cyrtoceras scoticum, Blake, PI. XXI. figs. 4, 4a. 



Type. — Section elliptic, with the shorter axis in the plane of curvature. Axes 

 at last in the ratio of 7 to 6. The curvature is great, the mean radius being about 

 7 lines. The rate of increase is 1 in 2 at first, but rapidly diminishes to zero in 

 the body-chamber. There are signs of the surface having had transverse rugosities 

 of growth, but on the whole it is smooth. The septa are direct, at a variable dis- 

 tance, on the average f the diameter. No siphuncle is seen. The initial point 

 is beautifully shown ; it has a cicatrix. The diameter of the whole shell is about 

 1 \ inches ; the diameter at the aperture is \ inch. From the Bala Beds of 

 Broughton. In the Museum of the Geological Survey, Edinburgh. 



General Description. — The type is unique. 



Relations. — In the great amount of curvature this is very near to Cyrtoceras 

 circumflexum and C. cycloideum of Barrande, but in the present case it is the short 

 and not the long diameter that is in the plane of curvature. Moreover, the septa 

 are much wider apart. 



Distribution. — In the Bala Beds, Broughton, Ayrshire (1). 



Cyrtoceras alternatttm, Blake, PI. XX. fig. 4. 



Type. — Section elliptic, diameters in the ratio of 9 to 8, and the long diameter 

 in the plane of curvature. The radius of curvature increases from 3^ inches to 

 6 inches. The long diameter increases at the rate of 1 in 6^. The surface is orna- 

 mented by transverse, rounded, not very separate ribs \ the diameter apart, alter- 

 nately larger and smaller, which run obliquely upwards towards the convex side, 

 making an angle of 4° with the axis of the shell. No finer ornaments are pre- 

 served ; but there are indications of possible fine longitudinal lines running over 

 the ribs. The specimen is all septate, but the surface of the septum is not seen. 

 The distance of the septa is ^ the short diameter. The sutures are straight and 

 rise to the convex side parallel to the ribbing, and lie in the hollow in front of the 

 larger rib. No siphuncle is seen. Length, 15 lines ; greatest diameter, 3^ lines. From 

 the Bala Beds at Bryn Bedwog, near Bala. In the Museum of Practical Geology. 



General Description. — The type is unique. 



2 b 



