60 



PISCES 



maxillae and sympliysial 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 



Diniclithys herzcri, Newberry. Diagrammatic front liew of upper and lower jaws, i/g. 

 Upper Devonian (Huron Shales) ; Delaware, Ohio (after NewberrjO- 



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. 



Titankhthys, 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 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 b}^ the lax'ge claviculars. 

 T. agassizi, ISF., 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. 



Homostcttjs millei-i, Traq. Crauial and dorsal sliield, i/g nat. 

 size. Lower Old Red Sandstone ; Caithness. .-1, B, C, Un- 

 determined bones ; ad!. Anterior dorso-lateral ; nc, Ethmoid ; 

 c, Central ; eo. External occipital ; m. Marginal ; md, Median Qccipital ' platC anterO-pOSteriorlv 

 doi-sal ; mo, >Iedian occipital ; o. Orbit ; pdl, Posterior dorso- ■, '- , ^ ,. nii r 



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

 behind " etliinoid " or rostral. The double lines indicate the fV.£> f>-.inl- l^i.^.Trlo,. fVinvi ^^,~,^, TT 

 course of the sensory grooves (after Traquair). inetlunK UlOdUei man long. XZ. 



milleri, Traq., from Lower Old Red 

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

 Livonia. 



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

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



