6 Mr. F. M'Coy on some new Fossil Fish 



again the osseous base thickens to form a little peltate mass. The 

 length of the portion preserved is 10 lines, width at base 3 lines, 

 broken extremity at the above length 1J line. 



From the red carboniferous limestone of Armagh. 



{Col. Capt. Jones, R.N., M.P.) 



Placodermi. 



I provisionally propose to establish a distinct family under the 

 above name, to include those Ganoid fish of the palaeozoic rocks 

 having the head and body encased in a series of odd or central, and 

 of subsymmetrical or lateral, bony, variously tuberculated plates 

 of large size. It might probably include all the genera described 

 by Agassiz in his l Monog. du Syst. Devon/ &c, under the title 

 Cephalaspides, except Cephalaspis, to which that family-name 

 might be retained, the other genera having no obvious affinity 

 with it ; in addition to these, the present group will conveniently 

 embrace the genera Bothriolepis, Asterolepis and Psammosteus, 

 which, although widely separated from the former by Agassiz 

 and placed by him in his family of Ccelacanths, are so obviously 

 and closely allied to some of them (e. g. Chelyophorus, Coccosteus, 

 &c), that they cannot be separated either by general appearance 

 or any points of structure with which we are acquainted ; while 

 they differ, on the other hand, from the other Ccelacanthi by the 

 body not being covered by imbricating scales. The teeth are 

 conical and plicated at the base. 



Osteoplax (M'Coy), n. g. 



Gen. Char. Dermal plates large, flat, osseous, polygonal, with 

 straight sides ; surface irregularly and minutely wrinkled, with 

 scattered pores. Microscopic structure: — vertical section show- 

 ing large, distant, cylindrical, branched, vertical tubes (? Ha- 

 versian canals) terminating in the pores of the surface ; the 

 spaces between these tubes containing numerous oval bone- 

 cells, rather more than their own length apart, from each of 

 which short radiating branches extend on all sides, about six 

 to the length of a corpuscle. Horizontal section : — large, cir- 

 cular, distant openings of the vertical tubes, with numerous 

 intervening minute, radiated, Purkinjean cells, the tubuli of 

 which do not anastomose with those of the adjoining cells in 

 either section. One species. 



Osteoplax erosus (M'Coy). 



Sp. Char. Bony plates 1 to 2 inches wide and about 1 line 

 thick ; edges square ; surface with close, short, irregularly 



