SUB-CLASS II 



OSTKACODERMI 



53 



pierced by a large, apparently branchial foramen. P. rostrata, Ag. sp. (Fig. 

 101), and other species from the Lower Old Red Sandstone of England, 

 Scotland, Rhenish Prussia, and Galicia ; also from the Upper Silurian of 

 Galicia, and probably from the Lower Devonian of Spitzbergen. 



Palaeaspis, Claypole (Holaspis, Lank, non Gray). Dorsal shield apparently 

 simple, without posterior spine; orbits merely forming notches. P. americana, 

 Clay., from Upper Silurian (Onondaga Group), Pennsylvania. P. sericea, 

 Lank, sp., from Lower Old Red Sandstone, Monmouthshire. 



Cyathaspis, Lank. (Diplaspis, Matthew). Dorsal shield consisting of a large 

 central disc ; two long and slender lateral cornua, which are notched anteriorly 

 by the orbits and pierced further back by the supposed branchial foramen, 

 and a short and broad rostral plate. C. ha nisi, Huxley and Salter sp., from 

 Upper Silurian (Ludlow Bone-bed and Passage Beds) of Herefordshire. C. 

 schmidti, Geinitz, from Wenlock Limestone of Isle of Gotland. Other species 

 from corresponding formations in Germany, Galicia, and New Brunswick. 

 The so-called Scaphaspis ludensis, Salter sp., from Lower Ludlow, Leintwardine, 

 probably belongs to this genus. 



Order 2. ANASPIDA. Traquair. 1 



Tubercles only on the head region, not fused into plates ; the calcifications probably 

 in part with bone cells. No paired appendages. 



Family 1. Birkeniidae. Traquair. 



External ornament, when present, tubercular. Branchial openings a series of 

 small perforations laterally placed. One small dorsal fin ; tail heterocercal. Upper 

 Silurian. 



Birkenia, Traq. (Fig. 104). Trunk irregularly covered with deepened 



Fig. 104. 



Birkenia elegans, Traq. Restored outline in side view, about nat. size. 

 Upper Silurian ; Lanarkshire (after Traquair). d, Dorsal fin. 



scales ; a series of large scutes along the ventral border. 



© © 



B. elegans, Traq. 



Upper Silurian ; Lanarkshire. 



Lasaniuspi licus, Traq. Restored outline, about nat. size. Upper Silurian ; Lanarkshire, 



r, Postcephalic rods; r', Chain of ossicles; v.s, Ventral scutes (after Traquair). 



Lasanius, Traq. (Fig. 105). Trunk naked, except immediately behind the 



1 Traquair, R. H., Report on Fossil Fishes collected by the Geological Survey of Scotland in the 

 Silurian Rocks of the south of Scotland (Trans. Roy. Soc. Eclinb. vol. XXXIX., with 5 pis.), 1899. 



