HOLOPTYCHIOID FISHES. 65 



In the family Holoptychiida?, e. g. Holoptyckius flemingi Holo- 

 (186, and fig. 36), the remains of which fish occur in the ptychius. 

 Upper Old Red Sandstone of Scotland and the Upper Devonian 

 of Belgium, the body is covered with overlapping cycloid 



& X ;srv 





^ 



Fig. 36. — Holoptyckius Jlemingi, restored. 



scales with a superficial layer of hard substance resembling the 

 enamel of teeth, and called vitro-dentine or ganoin. The pectoral 

 fins have a long, pointed, scaled a xis or lobe, the vertebral 

 column has no bony centra, the axis of the tail is slightly up- 

 tilted, and the vertical infoldings of the teeth are very numerous 

 and complex. 



In the family Rhizodontidas, represented in the exhibited series 

 by Eusthenopteron foordi (188, and fig. 37), a fish found in 

 the Upper Devonian of Canada, the scales are cycloid, like 

 those of Holoptyckius, the pectoral and pelvic fins are shorter 

 than those of the Holoptychian fishes, tbe vertebral column 

 has ring-like centra in some of the genera, the axis of the tail 

 is either straight or is slightly uptilted, the teeth are conical 

 and the vertical infoldings of the walls are comparatively 

 simple. 



Resembling tbe Rhizodontid* in the pectoral fins being obtusely 

 lobate, but differing in the scales being rhomboidal instead of 



F 



