﻿BRITISH FOSSIL CEPHALOPODA. 139 



The flattened indication of the first has a rate of increase of 1 in 33 ; but owing to 

 the obvious distortion which the specimen has undergone, no reliance can be placed 

 on the measurements. About 1 inch of body-chamber is seen without an end, nor 

 is any end seen in the second example. The surface of the latter may have been 

 a little rugose transversely towards the aperture, or the appearance may be due to 

 pressure. The septa have now an obliquity of 33° in one and of 45° in the other. 

 In the smaller they are -§- the diameter apart, but in the larger, at last, -^V only. The 

 siphuncle appears to be indicated by a nearly central festooning of the septa, where 

 they may be supposed to grasp it ; it is not very broad. The length of the smaller 

 is 2| inches, and the diameter of the larger | inch. From the Upper Tremadoc of 

 Grarth. In the Woodwardian Museum. 



General Description. — The specimens of this species have all suffered compression 

 and an unknown amount of contortion, and their surface may also be subsequently 

 crinkled ; the true characters of the species are therefore obscure. The rate of 

 increase is slow, but ranges in actual specimens between 1 in 8 and 1 in 31. The 

 body-chamber is not certainly seen. The septa are always oblique ; the amount 

 varies actually from 7° to 45°, and they vary in their observed distance from -^ to T 3- 

 the apparent diameter. The siphuncle is seen in one example to be nearly lateral, 

 but this is probably a matter of pressure i the rest show it central and moderate in 

 size, always supposing that the festoon in the septa indicates it. The largest is 

 3f inches long and f inch in diameter. 



Relations. — Though much variation occurs in actual specimens, there is nothing 

 to differentiate them definitely. The nearest approach to this species is made by 

 0. audax of the Bala Beds, but considering its unflattened state its rate of increase is 

 more rapid. If it were not for the obliquity of the septa, which after all may be 

 due to distortion, this species, in its slow growth, numerous septa, and . central 

 siphuncle, is well fitted to be the primeval form. 



Distribution. — The examples seen are from the Upper Tremadoc of Llanerch (1), 

 Garth (9), Tremanhere, St. David's (1), and a more doubtful specimen from Arenig 

 Beds, Portmadoc (1). 



It is also recorded by Dr. Hicks, from the Middle Arenig, Whitesand Bay. 



Orthoceras pertinens, Blake, PI. III. fig. 11. 



Type. — The shell is depressed, so that the section is elliptical and rather flat on 

 the surface exposed. The rate of increase of the long diameter is 1 in 10. The 

 surface exposed is without ornament, and the line of junction with the stone is 

 perfectly uniform. The septa are direct and have very little convexity ; the distance 

 is about \ the diameter. The siphuncle is central, and very moderate in size, but 

 there are signs of organic deposit about the necks. The length preserved is 



t 2 



