﻿BEITISH FOSSIL CEPHALOPODA. 145 



Orthoceras druidii, Blake, PI. XV. fig. 2. 



Type. — The shell is probably compressed, so that the diameters are as 10 to 9 ; 

 and there is some little curvature. The rate of increase is in the compressed form 

 1 in 5. The body-chamber is shorter than its basal diameter, if all is preserved, 

 and there is a contraction near the aperture, which is, however, probably due to 

 pressure; the cast is smooth. The septa are oblique 13°, rising towards the more 

 convex side, and are distant \ the diameter. Greatest diameter, 10 lines ; greatest 

 length, 2 inches. Prom the Bala Beds of Cerrig-y-druidion. In the Museum of 

 Practical Geology. 



General Description. — I am not certain whether any other specimens are known. 

 If the curvature is an essential feature, there certainly are not ; but there are some 

 examples with an oblique septa at the same proportionate distance, showing a much 

 slower tapering, and the siphuncle f- across the longer diameter. 



Relations. — The great obliquity of the septa sufficiently marks off this species, 

 and is the feature which renders it worth notice. 



Distribution. — In the Bala Beds of Oerrig-y-druidion (1), Bala (2), and Marsh- 

 brook (1). There is also a large example in the Museum of Practical Geology, 

 said to be from the Upper Ludlow of Radnor, showing an equal obliquity of septa, 

 which may, however, be due to contortion. 



Orthoceras ardvellense, Blake, PI. XII. fig. 1. 



Type. — The specimen is somewhat compressed, so that the outline is irregular, 

 being flattened on one side, and the diameters are in the ratio of 3 to 2. The rate 

 of increase of the long diameter is 1 in 8, and this includes the body-chamber, which 

 is about twice the length of its basal diameter ; but the aperture is not reached. The 

 septa are slightly undulating, but on the whole are direct across the broader surface. 

 Their distance is \ of the longer diameter. No siphuncle is seen : there are folds 

 across the middle of each chamber parallel to the septa. The length is 6 inches, 

 and the greatest diameter 2-| inches. In a brown ferruginous grit, said to be from 

 Ardwell, and of Bala age. In the Museum of Practical Geology. 



General Description and Relations. — No other example corresponding to this 

 having been met with, the species cannot be considered as satisfactorily established. 

 It belongs to the 0. imbricatum group, and is most like the specimen figured by 

 Phillips as 0. marloense ; but if the septa were really oblique, this should appear on 

 the flattened side. Moreover, the rate of increase is kept up in the body-chamber, 

 which it is not in 0. imbricatum. It therefore seems advisable to separate the 

 species, which may be considered as the precursor of the last-named. 



Distribution. — In the Bala Series, Ardwell (1). 



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