44 Proceedings of the Royal Physical Society. 



The anterior dorso-median is peculiarly broad in shape. 

 Its antero-lateral margin on each side first envelops the 

 anterior dorso-lateral, and is then overlapped by it, this rela- 

 tion of the plates to each other being thus suddenly reversed. 

 Behind this the posterolateral and posterior margins of the 

 plate are, as in Pterichthys and Bothriolepis, overlapped by 

 the posterior dorso-lateral and the posterior dorso-median ; 

 the last-mentioned plate shows posteriorly a prominent angu- 

 lar point, projecting over the hinder opening of the carapace. 

 On the underside the median ventral plate is extremely 

 small. The arms are short, slender, and pointed ; the plates 

 of the head, which is large, are not well enough preserved 

 to be readable. The outer surface of the body-plates is 

 minutely tuberculated, the tubercles often tending to con- 

 fluence in concentric lines. 



In the form of the carapace Microhrachius resembles Bothrio- 

 lepis^ but the arms are short, and the mode of articulation 

 of the anterior dorso-median plate is altogether peculiar. 

 Only the type species, Microhrachius Dickii, Peach, sp., is 

 known. 



I have no material at present to enable me to enter into 

 the discussion of Actinolepis, Ag., or Chelyophorus, Ag., of 

 which the former at least is pretty certainly Asterolepid, as 

 already noticed by Miller and Egerton ; and the discussion 

 of the general affinities of the group will form the subject of 

 a subsequent communication. 



List of Wokks eeferred to. 



(1.) Eichwald, E. von. — " Die Thier- und Pflanzenreste des 

 alten rothen Sandsteins und Berokalks im Novgorod- 

 schen Gouvernement," Bull. Sc. St. Petersbourg, 

 April 1840. 



(2.) Eichwald, E. von. — " Leth?ea Eossica," Stuttgart, 1860. 



(3.) Miller, Hugh.—" The Old Red Sandstone, or New Walks 

 in an Old Field," 1st edition, Edinburgh, 1841. 



(4.) Agassi z, L. — " Monographic des Poissons Eossiles du 

 vieux Gr^s Eouge," Neufchatel, 1845. 



(5.) M'Coy, r. — " On some new Fossil Fish of the Carboni- 



