FISHES OF THE OLD RED SANDSTONE. 



593 



Agass., and f. 4 of this plate in profile. It is a head in the same state of preservation as fig. 3 of C. 

 Lyellii; the impression only gives us the form of the head, none of the bones having been preserved. 

 We can however trace some details marking the generic character, and which are not discoverable 

 in the preceding species. I have named this fish C. rostratus, because the anterior portion of the 

 head is prolonged to a pointed snout. The eyes are placed much further backwards on the disk of 

 the head, nearly on the third posterior division, turned directly upwards, and still nearer each other 

 than they are in Cephalaspis Lyellii they appear to have had an oblong form (judging from the 

 slight impression left of the orbits). Behind these we find also the parieto-frontal crests, which 

 are very near each other and less projecting than those of C. Lyellii, and between which the occi- 

 pital crests begin to rise. This head is much longer than wide, and its sides lessening rapidly, 

 are more arched than the line which runs from the extremity of the snout to the neck, and which 

 rises into a central crest from the anterior third of the head to the orbit. At the anterior extremity 

 of this crest there is a triangular, longitudinal depression which may have been occupied by the 

 nostrils, which must have been very near the end of the snout, and very distant from the eyes ; on 

 each side of this depression are two elevated points (fig. 6, c c), which lead me to suppose the su- 

 perior maxillary bones were detached from the head, as in the genus Hyp op h tha Imus and some other 

 of the family Silures. These bones were perhaps prolonged in the form of barbs on the sides of the 

 head, and were inserted in the cavity formed by these elevated points. The piece denoted by o ap- 

 pears to be the ethmoid bone, rounded at its anterior edge, and in front of which the intermaxillary 

 bone formed the end of the snout and the reflected edge of the sides of the head. In this part of the 

 impression are seen some traces of this bone, the surface of which is striated longitudinally, while 

 its fracture presents a granulated structure. I. dwell particularly on this peculiarity, and especially 

 on the striated surface being seen distinctly as well as the granulous structure of the bone, in a 

 specimen which evidently belongs to the genus Cephalaspis. This circumstance, joined to that of 

 the lateral bones of the head being bent back towards the inferior surface, will facilitate the deter- 

 mination of the other species. Towards the region of the eyes are also seen two lateral prolonga- 

 tions, which appear to be the equivalents of the horns of the crescent of C. Lyellii. On the right 

 side of the head it is evident that the inferior surface is longitudinally striated ; on the left side 

 there is a portion of the bone, the surface of which is striated in the same manner ; on both sides 

 is seen the granular structure of the bone. On the posterior edge of the left side there is a portion 

 of the lateral divisions of the head uninjured, on the exterior surface of which may be observed 

 similar longitudinal striae, as on the impression of the inferior surface at the edge of its fracture. 

 Between these two surfaces we again discover the granulous structure of the bone, and distinctly 

 see that the striated surfaces are of a different substance ; that it is a coat of enamel covering the 

 bones of the head 1 ." 



3. Cephalaspis Lewisii, Agass. (PL 2. fig. 6.) Recherches, vol. ii. t. lb. fig. 8. 



Of this species M. Agassiz says, " The specimen here figured is the only individual yet known 

 to me of this species. It is a simple impression in relief of the head, on the sides of which there 

 are some traces of organic substance. This impression, moreover, is so little characteristic, that 

 it would be impossible to decide on the genus to which it belongs, if it did not present in some 



1 This species has at present only been found at Whitbatch, in the central portion of the Old Red Sand- 

 stone : Dr. Lloyd pointed it out to me, and stated from whence the specimen described was taken. — R. I.M-, 



