﻿BRITISH FOSSIL CEPHALOPODA. 195 



2 inches. , The greatest diameter is opposite the first -§■ of the body-chamber. The 

 mean rate of increase of the long diameter up to this point is 2 in 3. The length of 

 the body-chamber is f of the long diameter of its base. The general direction of the 

 apertures is horizontal, the surface on the dorsal side becoming quite horizontal 

 before the large aperture is reached. The total space occupied by the aperture is 

 about f the diameter. The small aperture is a nearly equal axed but transverse 

 ellipse facing horizontally ; the large aperture is divided into two branches, which, 

 with the passage, makes the figure of Y ; the ends of the branches have little circular 

 expansions. The passage and the branches are long and narrow and face upwards. 

 The whole is well separated from the outside by an upward growth of the shell. 

 The septa are nearly flat, and are distant ^ the longest diameter apart ; the last has 

 half the usual size. The sutures are deeply impressed and direct. No siphuncle is 

 seen. The length is 2f iuches, the greatest diameter 2 inches. From the Lower 

 Ludlow, Leintwardine. In the British Museum. 



General Description. — Two other specimens showing a similar aperture are 

 known, which agree in the general proportions and other characters, but are 

 not in a condition to throw any further light on the species. 



Relations. — The general shape of this species is singularly like that of G. 

 obovatum, but the characters of the aperture immediately distinguish them. Phrag- 

 moceras pavidum (Barr.) has a similar aperture, but it is not horizontal, and the 

 general curvature of the shell, especially on the ventral side, is much greater, so 

 that it may really be a Phragmoceras. A somewhat similar aperture is seen in 

 Gomph. neglectum, but the shape of the shell is different. 



Distribution. — In the Lower Ludlow at Leintwardine (2) and at Usk (1). 



Gomphoceras GRATUM, Barrande, PI. XXIII. figs. 1, 2, la. 



1865. Gomphoceras gratum, Barrande, ' Syst. Silur. de Boheme,' pi. 73, figs. 6, 7 ; pi. 82, 



figs. 13-16, p. 320. 



Type. — Section oval, the narrower end on the ventral side, the axes in the ratio 

 of 13 to 11 ; the longer one in the plane of symmetry. The general direction 

 of the shell is straight, and its contours elliptical, the mean radius of curvature 

 of both sides being 3 inches. The greatest thickness is at the base of the body- 

 chamber. On the septal portion the rate of increase is 4 in 7. The body-chamber 

 has a length equal to its basal diameter in the plane of symmetry. It does 

 not contract so rapidly as the septal part, but continues of nearly the same 

 diameter for some distance. The aperture is prominent, being produced and 

 surrounded by a constriction. Its general direction is inclined 10° from the 

 horizontal towards the ventral side, and it occupies -| of the greatest diameter. 



2 c 2 



