Homosteus, Asmiiss, compared lolfJt Coccosteus, Agassiz. 51 



burgh, I propose to iii.ike this, the most perfect specimen of 

 Homosteus which has ever been found, tlie text of the follow- 

 ing remarks on the genus. 



Along with Homosteus it may, however, be as well to 

 re-examine tlie structure of Coccosteus itself as a basis of 

 comparison. 



The reading; of the cranial buckler of Coccosteus is much 

 complicated by the fact that CL-rtain superficial grooves 

 belonging to the lateral-line system are very conspicuous 

 and apt to be mistaken for sutures, while the true sutures 

 are visible with difficulty, and can only be made out in 

 exceptionally well-preserved examples. They seem, indeed, 

 to have almost entirely escaped the observation of Agassiz, 

 as the lines on the head indicated on his restoration of 

 Coccosteus (" Old Red," tab. 6, fig. 4) belong almost without 

 exception to tlie lateral-line system. The figures given by 

 Hugh Miller {Quart. Journ. Geol. Soc., 1859, p. 129, and 

 " Footprints," 1st ed., fig. 11), in which he attempts to 

 reduce the plates of the cephalic shield of Coccosteus to the 

 same plan as that of the bones of the top of the head in the 

 Cod, are much better, inasmuch as many of the true sutures 

 are given ; but it is also too plain that he also looked upon 

 the superficial grooves as indicating the real boundaries of 

 the plates which he considered as the homologues of the 

 cranial roof-bones in osseous fishes. Pander's interpretation, 

 although his figures give both sets of lines on the upper 

 surface with considerable though not joerfect accuracy, is 

 correct only as regards the hinder part of the buckler, his 

 reading of the anterior half being hopelessly wrong, and 

 consequently his elaborate comparison with the arrangement 

 in Asterolepis falls to the ground. By far the most correct 

 restoration of the cranial shield of Coccosteus is that of 

 Huxley,^ in which he omits the superficial grooves altogether, 

 and in which the only faults I can find are of omission, viz., 

 the non-recognition of the median suture between the two 

 central plates which he letters as " frontal," and of the pair 

 of premaxillary bones on each side of that median bone in 

 front, to which he applies the name " premaxilla." 



1 Dec. Gecl. Survey, x., \\ 30. 



