60 MONOGRAPH OF DURA DEN. 



plates in the existing Sudis gigas of South America. The huge Megdlichthys 

 of our coal-fields, so common in the iron-band shales of Fifeshire, possessed 

 three of these glosso-hyal pillars, as if nature in her arrangements had made 

 size a condition of organic structure. These two plates in the holoptychius 

 and other Dura Den ganoids are moveable, and seem to have been constructed 

 so as to change their true signification, and especially, when dislocated with 

 a view to cover their edges, would serve as frontlets under the eyes. The 

 bones of the skull, in this as in all sauroid fishes, are united by closer sutures 

 than those of existing fishes. The vertebrae articulate with the spinous pro- 

 cesses by sutures, like the vertebrae of saurians ; and the ribs also articulate 

 with the extremities of the spinous processes. The caudal vertebrae have 

 distinct chevron bones, and the general condition of the whole skeleton is 

 stronger ahd more solid than in other fishes. 



The Teeth. — The family of fishes, including holoptychius under considera- 

 tion, have many characters in common with the class of reptiles, and among 

 these the teeth are more especially allied to the reptilian type. They are 

 striated longitudinally towards the base, and have a hollow cone within ; and 

 the bones of the palate are also furnished, as in that order, with a large appa- 

 ratus of teeth, their back edges terminating in a sharp point, which rendered 

 them singularly adapted to drag and to lacerate. Another provision, strongly 

 allied to the dentition of the lizard-type, consists in the manner in which 

 these teeth were inserted in the jaw, with their roots entangled and ramified 

 through the osseous substance, and thus indicating the violence with which 

 they could be sunk into the body of a living fish. There was a double row 

 or set of teeth in the lower jaw, consisting of three or more, larger, and others 

 much smaller and less acute, placed in the interstices of the bony matrix ; a 

 condition of arrangement existing likewise in the voracious family of the 

 megalichthys, and serving, not so much perhaps for mastication, as a provi- 

 sional apparatus for securing the slippery bodies of their prey when dragged 

 into the mouth. 



The Fins. — M. Agassiz, generally from incomplete specimens, but with his 

 usual skill and sagacity, had clearly defined the nature and positions of the 

 fin-organs in the genus Holoptychius ; and, where the information could not 

 be supplied by the specimens submitted, he had conjectural! y, but most accu- 

 rately, assumed what Nature herself must have done in the circumstances. 

 We have a remarkable instance of this in his succinct but lucid description 

 of the arrangement of the fins on the Holoptychius nohilissimus. " At pre- 

 sent," he says, " I only know of the ventral and base of the caudal fins, 

 which are visible on the magnificent specimen of the Holoptychius nobilissimus 

 in the collection of the British Museum, and which I have represented in 

 Plate 22.* The ventral fins are very much thrown back, the one far distant 

 from the other, and carried back on the sides of the belly to the anal opening. 

 They are small, composed of several rays, but they are not in good enough 

 preservation for me to give more particular details of their form and struc- 

 ture. The caudal has a strong radius, which leads me to suppose considerable 

 development of that locomotive appendage. The pectorals appear to have been 

 * Monographie des Foissons Fossiles du Vieux Gres JRouge, Chap., iv. Plate F. 



