56 



PISCES 



CLASS I 



Order 4. ANTIARCHA. Cope. 1 



Dermal armour fused info large plates on the head and abdominal region. Exo- 

 skeleton consisting of calcifications with bone corpuscles, and invested with a more or 

 less continuous layer of ganoine. Dermal sense organs occupying open grooves on the 

 exoskeleton. Dorsal and ventral shields consisting of several symmetrically arranged 

 pieces, and the head articulated with the trunk. Orbits close together. A pair of 

 paddle-like pectoral appendages, invested in dermal plates, articulated with the 

 anterior ventro-lateral plates of the trunk. Median fins not continuous. 



The bony plates of the Antiarcha consist of three layers with numerous 

 bone cells, the middle layer traversed by large canals and lacunae, while the 

 outer and inner layers exhibit a more compact texture. 



Family 1. Asterolepidae. Traquair. 



Exoskeleton robust and tuber culated. Dorsal and ventral shields of trunk firmly 

 united by the lateral plates. Interorbital piece not fixed. A pair of paddle-lih 

 appendages, completely encased in dermal plates, movably articulated by a complex 

 joint with the anterior ventro-lateral plates of the trunk. Tail heterocercal, and one 

 small dorsal fin. Devonian. 



Plerichthys, Ag. (Pterichthyodes, Bleeker), (Figs. 108, 109). From 3 to 20 



Fig. 108. 



Pterichthys milleri, Ag. Restoration from above (A), below (JJ), and in side view (C). Lower Old Red Sand- 

 stone ; Scotland, ap, Pectoral appendages ; j, Articulation ; op, Operculum ; orb, Orbit (after Traquair). 



cm. in length, with a small head, which is rounded in front, a broad and deep 

 trunk flattened below, and a scaly tail. The upper surface of the head is 



1 Pander, C. If., Die Placodermen des devonischen Systems. St. Petersburg. 1857. — Traquair. 

 R. H., Ann. Mag. Nat. Hist. ser. 6, vol. II. 1888 ; and Mon. Palaeont. Soc, 1S94. 



