b FISH OF THE CARBONIFEROUS PERIOD. 



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

 by Agassiz in bis ^ 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 PsammosteuSy 

 which, although widely separated from the former by Agassiz 

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

 and closely allied to some of them (e. g. ChelyophoruSy 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 Coelacanthi 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 

 flexuous smooth grooves visible to the naked eye, and with 

 distant, irregularly scattered oval foramina. 



The remarkable bony plates to which I have given the above 

 name vary in the number of their sides and the amount of the 

 angles at which they meet ; but the sides are always straight, 

 and the surfaces flat and of uniform thickness. It is clear, from 

 their form, that they cannot belong to the head, but must be 

 viewed as dermal bones, covering some part of the body of a 

 mailed fish. Of known genera they can only be compared with 

 Psammosteus of the old red sandstone, to one species of which, 

 the P. rneajidrinus (Ag.), the resemblance is particularly close, but 



