150 Powr'ie — On the Genus Cheirolepis. 



showing a rather prominent condyloid process, and tapering an- 

 teriorly. Both the upper and under jaws possessed a single row of 

 rather long, slender, conical, but unequally sized teeth, as described 

 by Agassiz. A slightly elongated, nearly rectangular plate, rather 

 narrowed anteriorly, and having the posterior angles rounded, 

 situated immediately behind the upper maxilla, may have represented 

 the operculum (3) ; this plate is, however, imperfectly preserved. 

 A stout, rather short, coracoid (4) may be described as consisting of 

 these parts; — a strong ovate umbonate plate, a quadrilateral elongated 

 plate, proceeding upwards from the posterior half of the ovate plate, 

 nearly at right-angles to its major axis, and a triangular plate, fitting 

 into the space between the anterior half of the former, and the an- 

 terior margin of the latter ; these three appear to have consisted of 

 only one bone, the seeming divisions being occasioned by a ridge 

 between the two latter, and a depression between these and the first. 

 Of the two principal jugular plates (5) one is entire, the other only 

 partly preserved ; they are rather small, elongated and triangular in 

 form, having their median sides straight, the lateral outer margin 

 slightly concave, and the posterior edge rounded convexly ; one of 

 these plates, imperfectly preserved, is shown in Agassiz 's figure 

 above referred to. The space between the principal jugular plates 

 and the lower jaw seems to have been occupied by a number of 

 elongated lateral jugular plates (6), these plates or rays increase in 

 length, but decrease in breadth posteriorly ; their exact number I 

 cannot give, but there had been at least eight or ten of them. There is 

 no vestige of a median jugular plate preserved, but from the position 

 and size of the principal jugular plates it seems probable that such 

 may have existed. Other cranial bones are exhibited in my specimens, 

 but too much displaced and imperfect for description. The other 

 characteristics of this genus are too well known and too accurately 

 described by Agassiz, and others, to require notice here. 



In his " Poissons Fossiles " Agassiz figures and describes two 

 species of Cheirolepis, viz. : Cheirolepis Trailli (vol. ii. p. 130, pi. 1 d, 

 and pi. 1 e, fig. 4), and Cheirolepis uragus (vol. ii. p. 132, pi. 1 e, figs. 

 1, 2, 3), and in the "Poissons de Vieux Gres Eouge," he adds 

 another, Cheirolepis Cumraingice (p. 45, pi. 12). In the "Annals of 

 Natural History " for 1848, Professor McCoy indicates, and in the 

 work on British Palasozoic Fossils, by him and Prof. Sedgwick, he 

 describes and figures three other species which he names Cheirolepis 

 macrocephalus (p. 580, pi. 2 d, fig. 3), Cheirolepis curtus (p. 580, 

 pi. 2 D, fig. 1), and Cheirolepis velox (p. 581, pi. 2 d, fig. 2). 



Several reasons occasion very much seeming variety in fossil 

 fishes, which, in reality, are identical ; and in determining genera, 

 and more especially species, these require to be well weighed and 

 carefully considered ; whilst, without going into the questio vexata 

 of the indefinite variation of species, it is, I believe, now allowed 

 by all naturalists, that species vary to a very considerable ex- 

 tent. That this cause has sadly hindered our list is well exem- 

 plified in Mr. Davidson's magnificent Monograph of British 

 Brachiopods, published by the Palseontographical Society, in which 



