30 OLD RED SANDSTONE FISHES. 



their existence. Professor Agassiz curiously misunderstood the nature of the scute in 

 his Cepli. rostratus, for he was able in the specimen figured in PI. IV, fig. 2, to find two 

 large dorsally placed orbits similar to those of Ccphalaspis Lycllii ; it is obvious enough 

 that these do not exist, while it is equally difficult to recognise the " ethmoid " spoken of 

 by him, as well in rostratus as in his Lloydii and Lewisii. 



The genus Pteraspis includes three species, limited to the Lower Old Red Sandstone, 

 two occurring in the Cornstones of the West of England, the other obtained in 

 Forfarshire. I have had specimens from Herefordshire, which may indicate other species ; 

 they are not sufficiently satisfactory to warrant further notice. 



1. Pteraspis Crouchii, Salter. PL III; PI. IV, fig. 5; PL VI, figs. 4, 7, 8 ; and 



PI. VII, figs. 4, 8, 11. -' 



Ptekaspis Ckouchti, Salter, MS. 



— — Lankester. Brit. Assoc. Rep., Trans. Sect., p. 58, 18G4. 



Derivation. — Named after the Rev. J. F. Crouch, of Pembridge. 

 Characters. — Scutum antice et postice attenuatum : rostrum longum et attenuatum ; 

 discus elongato-cordiformis, apice utrinque oblique truncato : spina longa : cornua lateralia 

 magna, crassa -. superficies superior rostri parsque inferioris striis curvatis parallelis ornatae, 

 superficies externa disci et partium orbitalium striis concentricis ornata. 

 Stratigrapltical Position. — Lower Old Red Sandstone (Cornstones). 

 History. — Specimens of this species in the Ludlow Museum have been named 

 Pt. Crouchii by Mr. Salter ; and this name I have adopted. This species was not known 

 to Prof. Agassiz. 



General Remarks. — This form of Pteraspis is distinguished by its long attenuated ros- 

 trum, and by the casts of its disc being shaped like an elongated " heart" truncated obliquely 

 on each side of the apex, and having a broad, deeply undulate anterior margin. The rostra 

 are frequently found detached from the rest of the shield, and I have seen no specimen 

 in which they themselves were attached to it : many specimens, however, show the cast of 

 the concave part of the rostrum, in conjunction with that of the orbital portions and disc 

 (the substance of the rostrum itself having in all probability broken away in the stone, 

 on account of the upward curve which it makes). One specimen belonging to Mr. 

 Humphry Salwey, of Ludlow, shows the striations and contour of the elongated rostrum 

 in connection with the cordiform shield; the specimen is the largest I have seen, and it 

 is probably owing to its mature age that the connection between rostrum and disc was 

 sufficiently strong to persist. It is from this specimen chiefly that the pointed long 

 rostra have been shown to belong to the cordiform discs. The part of the rostrum, 

 about half its whole length, which is striated both above and below, is thick and solid, 

 and presents a considerable development of the layer of polygonal cavities within. Its 



