CEPHALASPIDtE. 



47 



species {C. Powriei), and hence we may consider the distinction, so far as it rests on tlie 

 form of hcad-shiehl, a good one. Some small specimens, as that drawn in PI. VIII, 

 fig. 5, wdiich probably belong to this species, show an outline rather like some small Scotch 

 heads I have seen, one of which is drawn in PI. XII, fig. 1. But the eyes are not so far 

 forward in the Scotch specimens as in the Enghsh, and we may conclude that they belong 

 to C. LyeUii, whilst the English ones belong to C. Agassizii. The Scotch member liad ' a 

 longer liead' than the English representative, even among these fishes of the Devonian 

 times. 



No bodies of C. Agtmizii appear to have been ever found attached to the heads, with 

 two exceptions, one of which is obscurely drawn in PI. VIII, fig. 5, whilst the other shows 

 little beyond the fact of a scale-covered body. Both specimens are very small, and, indeed, 

 may not belong to this species at all. They are from the Cornstones in the neighbour- 

 hood of Ludlow. Small specimens of scales, exhibiting a fine tubercular ornament like 

 that of the head-shield of C. Agassizii, have been found, but give no evidence as to the 

 form or relative proportions of the body. It is not a little remarkable that in the Corn- 

 stones of Herefordshire and in the slaty beds of Devonshire and Cornwall — which have 

 lately (1SG8) been shown to contain CephalaspidcB — the smallest traces of the body, well 

 covered in by scales, as we know it to have been, should be so exceedingly rare as com- 

 pared with the head-shields, which abound in the AVest of England, and are packed and 

 pressed together in innumerable quantities in Cornwall. The relative size and weight of 

 head and body, no doubt, favoured the preservation of the head-shields, which, like the 

 Belemnite's guard, would sink, whilst the body would be broken off from the thus partially 

 imbedded head. The large size and freedom from open sutures of the adult head-shields 

 would also, no doubt, tend to their preservation, as compared with the smaller and 

 therefore more easily scattered scales. A strange instance of the capricious imperfection 

 of that very fragmentary document, the ' Geological Record,' is afforded in the absence of 

 bodies to English Cephalaspids, and their more frequent occurrence in Scotch specimens. 



3. EucEPHALASPis PowKiEi. PI. X, fig. 1, aud PI. IX, fig. 5. 



Cephal.vspis Lyellii, A(/assiz (in part). Pois. foss., vol. ii, pi. 1, fig. 1, and pi. 1 b, fig. 1, 1835. 



Name. — After Mr. Powrie, of Reswallie, Eorfarshire, the discoverer of this and other 

 Cephalaspids. 



Stradgrajjhical Position. — Lower Old Red Sandstone of Eorfarshire. 



Characters. — The form of head-shield distinguishing this species is given iii the 

 diagram (woodcut, fig. 19). A form of curve which it is difticult to describe in 

 words, but which might be expressed mathematically, distinguishes the contour of the 

 shield of this form from those of the two preceding. The cornua have a difierent relative 



