62 MONOGRAPH OF DURA DEN. 



edge, and in exhibiting three well-marked zones, which are smooth in front, 

 and covered with rounded tubercles behind. The most clearly defined 

 distinction in Holoptychius nuhilissimus consists in the size and general 

 roughness of the scales, which are very large on the middle of the belly, and 

 become arched in diminishing gradually towards the tail. In Holoptychius 

 giganteus the scales are very thick, of a rounded form, resting on smooth 

 zones, and beautifully ornamented on the inferior side, as in the medullar 

 lines and osseous supports of the Glyptolepis leptopterus. Holoptychius Oma- 

 liusii is distinguished from all the above specific forms in the enormous 

 magnitude and thickness of the scales, which are deeply furrowed, with lon- 

 gitudinal and parallel ridges, which, from their fine irregular granulation, give 

 the appearance of shagreen; and, above all, by the size of a body that must 

 have attained the length of at least twelve feet ! This fossil, but very 

 imperfect, has only been found in one locality, namely, in the Old Eed of the 

 neighbourhood of Namur, by M. Omalius de Halloy. The other five species 

 belong to Dura Den and Clashbennie. 



The specimen on which was determined the species — Holoptychius Ander- 

 soni — was the first discovered of the genus in anything like completeness, 

 and was figui'ed, in 1837, in my Geological and Botanical Description of 

 Fifeshire. The large specimen discovered in 1858, along with the massive 

 caudal fins, on another tablet of rock, completes the entire equipments of this 

 c^lacanthic fossil, showing it in full outline and perspective, and producing 

 as perfect a restoration of a form of extinct life as any in the annals of geo- 

 logical discovery yet recorded. The massive dimensions to which it has 

 attained, and corresponding magnitude of the scales, show a very considerable 

 affinity and resemblance to the Clashbennie Holoptychius nobilissimus, but 

 besides many minute discrepancies in the granulation of the cephalic bones 

 and the ridgy eminences on the scales, the Dura Den fossil justifies its claims 

 to a specific honour, upon the ground of its occupying a position in the 

 upper series of the system, and thus standing so much higher in the order of 

 stratigraphical arrangement, and so much later in the geological horizon of 

 animal life. 



Holoptychius Nobilissimus. — Aqassiz. 



