﻿132 BEITISH FOSSIL CEPHALOPODA. 



out, and in the specimen examined the part preserved is actually narrower, and the 

 imbrications towards the smaller end are more remote in proportion than in the 

 type. No other species imitates this closely enough for useful comparison. 



Distribution. — In the Lower Llandeilo of Cefh Gwynlle, Shelve (6), Bogmine (2). 

 Grit mine (1) ; in the Upper Llandeilo of Abereiddy (2) ; in the Upper Arenig of 

 St. David's (3). 



Dr. Hicks also records this from beds of similar age at Carnarvon. 



Orthoceras ascendens, Blake, PI. XII. fig. 7. 



Type. — The section is circular, and there is a slight curvature of the shell ; the 

 rate of increase is 1 in 15. The ornaments are sharp, upward imbrications which 

 cross the shell directly, without any undulation ; they are distant about \ of a line 

 or _]^ the diameter. The septa are not seen, but the siphuncle appears to be 

 central. The diameter is 2 lines and the length 11 lines. From the Bala Beds 

 of the Chair of Kildare. In the Museum of Practical Geology. 



General Description. — Associated specimens, one perhaps the actual continuation 

 of the type, show the curvature continued to near the apex, and the rate of increase 

 as much as 1 in 11. The direct upward imbrications are from 18 to 6 per line, 

 according to the diameter, but in proportion to the latter line they are closer in 

 larger specimens. No further details of septa or siphuncle have been seen. The 

 largest fragment has a diameter of 4 lines. With this species may be temporarily 

 associated a specimen from the Upper Silurian, which has similar direct upward 

 imbrications, rather approaching in character to grooves, distant £ line and parallel 

 to the septa, the last four of which are but -^ the diameter apart. The body- 

 chamber slightly contracts towards the aperture. This may well be a distinct 

 species, when all data of the present one are known. 



delations. — This species is separated from 0. subundulatum on the ground of 

 the upward imbrications being direct and not undulating, in which also it differs 

 from 0. advena ; the ornaments are also closer, and the rate of increase less than in 

 the former. It is nearly allied to 0. primum, Barrande, but its rate of increase is 

 less, and it is a smaller shell and has a central siphuncle ; it is also curved. 



Distribution. — In the Bala Beds of Kildare (3), and Knockshligon, co. Tip- 

 perary (1) ; in the Lower Ludlow of Ledbury, doubtfully. 



