SÜB-CLASS II 



OSTRACODEKMI 



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. 



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

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

 Glay., 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. banksi, 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. AN ASPIDA. Traquair.^ 



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

 in pari with bone cells. No paired appendages. 



Family 1. Birkeniidae. Traqiiair. 

 Exteriml ornamenf, when present, tubercular. Branchial openings a series of 



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

 Silurian. 



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



Fig. 104. 



Birkenia elegans, Traq. Restored outline in side view, aboiit nat. 

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



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

 Upper Silurian ; Lanarkshire. 



B. elegans, Traq. 



Fig. 105. 



Lasonitis problematiciis, Traq. Restored outline, about nat. size. Upper Silurian ; Lanarkshire. 



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



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



^ Traquair, R. JH., Keport on Fossil Fishes collected by the Geological Survey of Scotland in the 

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



