72 PISCES. 



Three families of Rhipidistia are distinguishable, and of 

 these it is noteworthy that the Holoptychiidse, with acutely 

 lobate pectoral fins, are the oldest. These, at least, are not 

 known to range above the Upper Devonian, whereas the Rhizo- 

 dontidaB and Osteolepidas, though appearing equally early so 

 far as known, seem to have attained their maximum specializa- 

 tion in the Carboniferous, and one genus of the latter survives 

 even in the Lower Permian. 



The Holoptychiidae, or Dendrodontidae, as they are 

 sometimes termed in allusion to the complicated structure of 

 the teeth (fig. 54, p. 70), are represented only by the typical 

 genus Holoptychius and the essentially identical Glyptolepis. 



FIG. 55. 



Holoptychius flemingi ; outline restoration by ~R. H. Traquair, one-eighth nat. 

 size, the ornamentation omitted U. Old Ked Sandstone ; Dura Den, 

 Fifeshire. 



Holoptychius (figs. 19, 55). A round-bodied fish, covered with thick, 

 deeply overlapping, cycloidal scales, which are ornamented in their exposed 

 portion with irregular wrinkles and ridges of ganoine. The head is com- 

 pletely invested with dermal and membrane-bones, which are ornamented 

 with tubercles and rugae of ganoine. The parietals are large and separate ; 

 the frontals are also separate, not fused into a continuous plate with the 

 adjoining elements, and there is no parietal or frontal foramen. The 

 dentary bone of the mandible is thin and deep, bearing a series of small 

 teeth, and with well-developed infradentaries which turn inwards below ; 

 the splenial is subdivided into a series of large, broad, shuttle-shaped 

 bones, each supporting a large tooth. The operculum and suboperculum 

 are present, but the preoperculum and interoperculum seem to be wanting. 

 The gular plates entirely cover the space between the mandibular rami, 

 comprising one large pair flanked on either side by a small lateral series. 

 No ossifications have been observed in the notochordal sheath. The pec- 

 toral fins are long and acutely lobate, but the pelvic fins are much shorter 

 with an obtuse lobe ; the supporting cartilages are unknown. There are 



