60 



PISCES 



CLASS I 



maxillae and synrphysial 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 



Pig. 112. 



Dinichthys Jierzeri, Newberry. Diagrammatic front view of upper and lower jaws, 1 fe. 

 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, Xewb. 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 horn. 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 



Fig. 113. 



Homosteus milli ri, Traq. Cranial and dorsal shield, i/e lia t- 

 size. Lower Old Red Sandstone; Caithness. A, B, C, Un- 

 determined bones ; adl, Anterior dorsolateral ; etc, Ethmoid; 

 c, Central ; eo, External occipital ; m, Marginal ; md, Median occipital plate ailterO-pOSteriorlv 

 dorsal ; mo, Median occipital ; o, Orbit ; pdi, Posterior dorso- , . -, -,. -iii r 



lateral; po, Preorbital; pto, Postorbital. Pineal plate elongated; median dorsal plate 01 

 behind " ethmoid " or rostral. The double lines indicate the 4.U +r , m i. l-M-norlm- +Vmn lnno- 77 

 course of the sensory grooves (after Traquair). tneLiUiiK uioduei uiiciii iun^,. xx. 



millerij Traq., from Lower Old Eed 

 Sandstone, Caithness and Orkney. Other species in Upper Devonian of 

 Livonia. 



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

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



