CEPHALASPID^. 25 



extend in a longitudinal direction from near the frontal margin, and converge towards the 

 spinous termination of the ovoid scute ; these are interstriated by the fine grooves charac- 

 teristic of all Heterostraci: The space in front of the origins of the longitudinal 

 ridges is transversely striated and somewhat thickened, indicating the rostral region, as 

 in other Scaphaspids. 



Distribution. — The only locality at present known for this species in the Downton 

 Sandstone is Kington, Herefordshire. I have seen a fragment in a slab from the 

 Ludlow Bone-bed. 



4. ScAPHASPis LuDENsis [Salter). PI. II, figs. 4, 4 a. 



Syn. Pteeaspis Ludensis, Salter. Annals and Mag. Nat. Hist., 3 ser., vol. iv, p. 45, 

 woodcut, fig. 1, 1859 



Derivation. — Ludensis, belonging to Ludlow. 



Characters. — Scutum elongatum, oblongum, ovato-quadrangulare, antice et postice 

 truncatum, postice spina brevissima armatum ; superficie externa coUiculis longitudinalibus 

 rectis antice transversis, non interstriatis ornata. 



8trati(/raphical Position. — This species has been found in both the Lower and the Upper 

 Ludlow beds. 



History. — Mr. Salter, in 1859, described this fish-shield from specimens obtained by 

 Mr. Lee and Mr. Robert Lightbody, of Ludlow. 



General Remarks. — This, the oldest vertebrate animal of which traces have been 

 met with, is known by but a very few imperfect specimens. It was first obtained from 

 the Upper Ludlow deposits, but was afterwards detected near Leintwardine, in Shropshire, 

 by Mr. Lee, in the Lower series bearing that name ; this discovery added enormously to the 

 age of the fossil. 



The form of the scute in Scaphasjns Ludensis is that of a much elongated ellipse 

 truncated at both ends, the small spinous tubercle situated near the posterior margin of 

 the shield hardly projecting beyond it. Like that of Sc. truncatus, the spine is the ter- 

 mination of a lightly marked central ridge ; and, as in that species, the inner surface of 

 the shield exhibits indications of this ridge and of the coarse longitudinal furrowing of 

 the outer surface. As Sc. rectus resembles Sc. Lloydii in many points, but differs in 

 being much narrower, and in not terminating acutely behind, so does Sc. Ludensis 

 resemble and differ from Sc. truncatus. The ornamentation on the outer surface of the 

 shield is in the form of straight longitudinal ridges and furrows, coarser than in other 

 Heterostraci. These ridges do not converge, but run parallel from one end of the 

 shield to the other, a small frontal portion being left which is transversely marked. The 

 length of the largest scute I have seen is about one inch and a half. 



Localities. — The neighbourhood of Ludlow ; and Church Hill, Leintwardine. 



4 



