﻿CEPHALASPJD^. 185 



Cephalaspis murchisoni, Egerton. 

 [Plate IX. fig. 6 ; Plate X. figs. 1-4.] 



1857. Cephalaspis murchisonii, Sir P. Egerton, Quart, Journ. Geol. Soc. 



vol. xiii. p. 284, pi. ix. fig. 1. 

 1857. Cephalaspis ornatus, Sir P. Egerton, ibid. p. 285, pi. ix. figs. 2, 3. 



[Imperfect shield ; British Museum.] 

 1870. Hemicyclaspis murchisoni, E. K. Lankester, Fishes Old Red 



Sandst. pt. i. (Pal. Soc), p. 51, pi. viii. fig. 6, pi. ix. fig. 1, pi. xiL 



figs. 3, 4. 



Type. Shield ; unknown. 



The type species of the subgenus Hemicyclaspis, of moderate size. 

 Shield sharply rounded in front; orbits placed nearly midway 

 between the anterior and posterior margins ; cornua rudimentary. 

 Superficial ornamentation consisting of widely spaced, regularly 

 arranged, large tubercles, with intervening small tubercles. Scaly 

 trunk about three times as long as the shield. 



Form. Sf Loc. Ludlow Tilestones and Lower Old Red Sandstone 

 Passage Beds : Herefordshire. 



The specimens presented by George H. Piper, Esq., recorded below 

 and shown in the accompanying Plates, make known the exoskeleton 

 of this species almost completely, and add important items to our 

 knowledge of the morphology of the Cephalaspidians in general. A 

 restoration is attempted in the woodcut (fig. 24), and the following 

 are detailed notes on the collection. 



Fig. 24. 



Cephalaspis murchisoni, Egert. — Side view, restored from specimens discovere 

 by George H. Piper, Esq. [Nos. P. 6023, &c.J 



The precise form and proportions of the anterior shield have 

 already been determined by Lankester (fig. 25), and the fossils under 

 discussion are quite similar to those previously studied. The absence 

 of posteriorly prolonged cornua is distinctly shown ; there is the 

 well-defined high " posterior ridge "behind the " postorbital valley,'* 

 and the usual three layers entering into the constitution of the shiel 

 are readily distinguishable. There is also no trace of sensory 

 canals. 



