﻿200 BRITISH FOSSIL CEPHALOPODA. 



seen. The surface had only rough lines of growth. The septa have a convexity of 

 ^ their long diameter, and are distant -|- the mean diameter. The sutures are 

 slightly undulating, but on the whole direct. The siphuncle is not seen ; but, the 

 convexity having been cut and polished to find it, it is certainly not external. 

 Length, 2i inches ; greatest diameter, l-i- inches. From the Bala Beds of Rhiwlas. 

 In the Museum of Practical Geology. 



General Description. — Another specimen from the same locality shows some 

 contraction to the aperture, and may therefore belong to this species. Its general 

 shape and rate of increase are the same, as also the septal characters ; but its curva- 

 ture is less, the mean radius being nearly 3 times the corresponding diameter. 



Relations. — There is great similarity in appearance between this and Cyrtoceras 

 intermedium of M'Coy ; but this is an undoubted Phragmoceras, a fact of very 

 considerable interest, as being only the second species recorded from the Lower 

 Silurian of Europe, P. rectiseptatum of Romer being the other. 



Distribution. — In the Bala Beds, Rhiwlas, Bala (2). 



Phragmoceras ventricosum, Sowerby, PI. XXIY. figs. 1, la, 2, 2a, 3. 



1838. Phragmoceras ventricosum, Sowerby in Murchison's ' Silurian System,' pi. 10, 



figs. 4, 6 (not fig. 5). 

 1852. „ „ M'Coy, ' Palaeozoic Fossils,' p. 322. 



Type. — Section an elongated ellipse, the longer axis in the plane of curvature. 

 Ratio of axes 2 to 1, which may be more or less due to pressure, as it is less on the 

 septal portion. Mean radius of curvature about 3^ inches, when the mean diameter 

 is 3 inches. Rate of increase decreasing from 1 in 2 to 1 in 9. The body -chamber 

 has a length equal to the longer diameter (now compressed) of its base. The aperture 

 is nearly closed for some distance above the central line, but owing to compression 

 the true shape of the opening cannot be seen. The shell has a uniform ornamen- 

 tation of fine ribs about 10 per inch on the side, curving backwards and so convex 

 towards the aperture ; more irregular at last. The septal convexity is not great. 

 The sutures are sigmoidal, curving back in the middle of the side, but on the whole 

 direct, and about y 1 ^ the diameter apart on the outside. The siphuncle is not seen 

 with perfect distinctness, but appears to be internal and bulbous. Length, 6j inches ; 

 greatest diameter, 3i inches. Associated with this specimen is another, also figured 

 by the author of the species, which has an irregular aperture in which the large 

 opening is transverse, but not produced. From the Lower Ludlow of Aymestry. 

 In the Museum of the Geological Society. 



General Description. — The shells of the Phragmocerata seem to have been but 

 weak ones, and they have accordingly given way under pressure to a very 

 puzzling extent, and we have no very reliable determination of the true shape and 



