502 Dr. K. H. Traquair on the 



him Pterichtliys Dichii'^j shows some pecuHavities which 

 seem to me to be decidedly of generic value. 



It is small in size, head and carapace together measuring 

 only about l^ inch in length. In shape it resembles Bothrio- 

 lepis, having the carapace generally depressed and broader on 

 the upper than on the under surface. On the upper surface 

 the anterior margin of the carapace forms a deep reentering 

 angle (see PI. XYIII. fig. 8) or emargination, so that the 

 antero-external angles of the anterior dorso-lateral plates 

 project considerably in front. 



The anterior dorso-median is peculiarly broad in shape. 

 Its antero-lateral margin on each side first envelops the an- 

 terior dorso-lateral, and is then overhipped by it, this relation 

 of the plates to each other being tlius suddenly reversed. 

 Behind this the postero-lateral 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 

 he 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 Bo~ 

 thriolejns, 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 JVLiller and Egerton ; and the discussion 

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

 a subsequent communication. 



List of Works referred to, 



(1) EiCHWALD, E. VON. — " Die Thier- und Pflanzenreste des alten 

 rothen Sandsteins und Bergkalks ini Novgorodschen Goiiverne- 

 meiit,'' Bull. Sc. St. Petersbourg, April 1840. 



(2j EiCHWALD, E. VON. — ' Lethaea Rossica/ Stuttgart, 1860. 

 * British Assoc. Rep. 1867. 



