60 



PISCES 



CLASS I 



maxillae and symphysial end of mandibular bones with a pair of stout cusps or 

 beaks, and the trenchant margin behind these sometimes toothed. Median 

 dorsal plate very thick, often over 0*6 m. long and broad. Antero-dorso-lateral 



Fig. 112. 



Dinichthys lierzeri, Newberry. Diagramm atic front view of upper and lower jaws, i/g. 

 Upper Devonian (Huron Shales) ; Delaware, Ohio (after Newberry). 



plate overlapped by the large " clavicular." Several species in the Middle and 

 Upper Devonian of Iowa, Wisconsin, Ohio, New York, and Canada ; others 



in the Devonian of the Eifel, 

 Bohemia, and Russia. 



Titanichthys, Newb. Cranial 

 shield very large, thin and 

 flattened, arrangement of plates 

 closely similar to that of Din- 

 ichthys. Jaw elements much 

 reduced, edentulous, probably 

 sheathed in hörn. Dorso-median 

 without an inferior longitudinal 

 keel, deeply emarginate in front. 

 Antero- and postero-dorso-laterals 

 fused, articulated to the cranial 

 shield by a long hinge, and over- 

 lapped by the large claviculars. 

 T. agassizi, N., has a horizontal 

 expanse of 1*9 m. across head- 

 shield and claviculars. Cleveland 

 Shale (Upper Devonian) ; Ohio. 



Homosteus^ Asmuss. (Fig. 113). 

 Very large fishes, broad and de- 

 pressed. Orbits completely en- 

 closed in the head shield ; jaws 

 slender and toothless. Median 

 occipital plate antero -posteriorly 



Fig. 113. 



Homosteus milleri, Traq. Cranial and dorsal shield, i/g nat. 

 size. Lower Cid Red Sandstone ; Caitlmess. A, B, C, Un- 

 determined bones ; adl. Anterior dorso-lateral ; ae, Ethmoid ; 

 c. Central ; eo, External occipital ; vi. Marginal ; md, Median 



dorsal ; mo, Median occipital ; o, Orbit ; -pdl. Posterior dorso- , ^ , , . , ^ ^ , r 



lateral; po, Preorbital ; pto, Postorbital. Pineal plate elongated ; median dorsal plate Ol 

 behind ''ethmoid " or rostral. The double lines indicate the f}ip f^nnlr hrnn rl Pr fVinn Inner TT 

 course of the sensory grooves (after Traquair). LUetlUIlK Uiuauei tuan iOIlü. xi. 



the trunk broader than long. 



milleri, Traq., from Lower Old Red 



Other species in Upper Devonian of 



Sandstone, Caithness and Orkney. 

 Livonia. 



Heterosteus, Asmuss. Nearly resembling Homosteus, but larger, and anterior 

 dorso-lateral body plates with an enormous anteriorly directed process which 



