﻿196 BEITISH FOSSIL CEPHALOPODA. 



The ventral opening is small, and transversely elliptical. The dorsal opening has 

 three lobes on each side, increasing in size as we go from the ventral side ; the 

 dorsal boundary is concave. The passage is short and narrow. The dorsal opening 

 faces upwards from the apex of the shell, but the ventral horizontally. The shell 

 had lines of growth which made a pointed sinus backwards on the ventral side. 

 The base of the body-chamber is crenulated. The septa have little convexity, and 

 are distant -j- 1 ^ the greatest diameter. The sutures are horizontal. The siphuncle is 

 situated -g- the diameter from the ventral side on the long diameter. Its diameter 

 is -jt that of the shell, and it is inflated between the septa. Greatest length, 

 2§ inches ; greatest diameter, 1^ inches. From stage E, or Upper Silurian, of 

 Bohemia. 



General Description. — The British specimens which show the remarkable 

 aperture of this species are but few in number. They are all more or less 

 distorted by pressure. The section is probably nearly circular, and is made 

 transverse or otherwise by compression, the diameters not being more unequal 

 than as 11 to 10. The amount of curvature cannot be told, but it is about the 

 same as in the type and nearly equal on both sides, the general direction being 

 straight. The rate of increase is less than 2 in 3 on the septal portion. The 

 body-chamber has a length of § its greatest diameter at the base, and slowly 

 decreases. The aperture, which is surrounded by a constriction, has suffered much 

 and obvious distortion in every case, and the resulting forms have rather a different 

 appearance, the shell in one (fig. 2) coming to a sharp point at the dorsal 

 opening ; in this case it shows three lobes on each side, increasing in size towards 

 the dorsal side, but less unequal than in the type. The dorsal border is concave ; 

 the passage is short and narrow ; the ventral opening is elliptic, with the long axis 

 in the plane of symmetry, and is of fair size ; it faces perpendicularly to the slope, 

 which is now 30° from the horizontal. How much of this is due to distortion is 

 not certain, but from another specimen, compressed on the side instead of drawn 

 out, the ventral aperture makes but little show, and the lobes of the dorsal one are 

 hard to make out, though present (fig. 1). The surface has fine lines of growth 

 coming to a pointed apex on the ventral side, and the base of the body-chamber 

 is crenulated. The septa have a convexity ^ their diameter, and are distant -^ the 

 greatest diameter. The sutures are direct. The siphuncle is now unsymmetrically 

 placed, nearly on the shorter diameter, at a distance equal to its own diameter from 

 the ventral side; it is rather elliptic, with its longer diameter in the plane of 

 symmetry. Greatest diameter, 22 lines. 



There are thus several differences between our specimens and the type, which 

 differences however are just in those characters that might be altered by distortion, 

 while in all other points, especially in those independent of pressure, there is a 

 remarkable agreement. 



