﻿188 BRITISH FOSSIL CEPHALOPODA. 



very close resemblance to Portlock's specimen, but the body-chamber continues to 

 increase towards the aperture instead of decreasing. 



Distribution. — In the Bala Beds of Piedmont, Ayrshire (1), and of Desert- 

 creat (1). 



Genus GrOMPHOCERAS. 



GtOMPhocbras iEQUALE, Blake, PI. XXVI. figs. 6, 6a, 6b. 



1873. Gomphoceras .equale, Salter, ' Camb. and Sil. Fossils,' p. 160 (name only). 



Type. — Section nearly circular, the longer diameter in the plane of symmetry. 

 General direction straight, the two sides gently and equally convex. The body- 

 chamber commences at or before the greatest diameter, and converges towards the 

 aperture. Its length is •§ the basal diameter ; the aperture is produced, with a con- 

 striction round it ; the ventral opening is not separate from the passage, which is rather 

 wide ; the dorsal opening is a transverse ellipse, with a minor axis a little larger than 

 the diameter of the passage, and the major twice the minor. The septa are very flat, 

 and at a distance of about \ the greatest diameter. The sutures are slightly undu- 

 lating, and the siphuncle small and central. Greatest length, 20 lines ; greatest 

 diameter, 14^ Hues. From the Wenlock Limestone, Dudley. In the Woodwardian 

 Museum. 



General Description. — The section is to a certain extent dependent on pressure, the 

 axes varying from equal to a ratio of 2 to 1, but the longer one always in the plane 

 of symmetry, showing that the true shape is more or less elliptic in that direction. 

 The general direction of the axis of the shell is straight. The curvature on each 

 side is slight, forming part of an ellipse with axes of about 2 inches and 1^ inches. 

 Thus the body-chamber and the septal portion alike have curved outlines. The rate 

 of increase is greater than 1 in 2. The body-chamber is from f to f the basal 

 diameter in length. It becomes elliptic at the top, even if. the septal section is cir- 

 cular. The aperture occupies the top, and has a general horizontal direction. Its 

 pattern in all agrees with that of the type. The septa are very flat, so that the 

 shell looks truncate at the end. They are distant from ^ to -|- the greatest diameter. 

 The sutures are direct, but slightly undulating ; the siphuncle is small, and either 

 central or a little excentric on the long diameter towards the ventral side. The size 

 is always small ; the largest is 3 inches long by 2 inches, but they are seldom much 

 more than 1 inch in diameter. 



Relations. — This small species repeats many of the characters of G. ellipticum. 

 It has the same general shape, though the curvature of the sides is less than in the 

 latter. Its aperture is of the same type, though less complicated ; yet we cannot 



