﻿204 AN XI ARCH A. 



with tubercles ; [tail unknown]. Lateral sensory canals upon the 

 upper aspect of the head united by an anterior transverse commis- 

 sure crossing the premedian plate, and by a posterior one directly 

 crossing the median occipital ; anterior median dorsal plate over- 

 lapping both the anterior and posterior dorso-laterals. Pectoral 

 appendages shorter than the armoured trunk, segmented into a 

 distal and proximal portion. 



This genus is only known from isolated dermal plates so similar 

 in form to those of Pterichthys as to have induced C. H. Pander ] to 

 regard the last-mentioned name as a synonym. The only un- 

 doubted distinguishing feature, according to R. H. Traquair 2 , is the 

 mode of overlapping of the anterior median dorsal plate. The tail, 

 however, is still unknown. 



Asterolepis ornata, Eichwald. 



1840. Astrolepis, E. Eichwald, Bull. Sci. St.-P6tersbourg, vol. vii. p. 79. 

 1840. Asterolepis ornata, E. Eichwald, Neues Jahrb. p. 425. 



1844. Asterolepis ornatus, E. von Eichwald, Bull. Soc. Imp. Nat. 

 Moscou, vol. xvii. p. 829. 



1845. Asterolepis ornata, L. Agassiz, Poiss. Foss. V. G. R. p. 93, pi. B. 

 fig. 4 ; pi. xxx. figs. 2-9 (? in part). 



(?) 1845. Asterolepis apicalis, L. Agassiz, op. cit. p. 148, pi. xxxi. a. 



fig. 31. 

 1857. Asterolepis, C. H. Pander, Placoderm. devon. Syst. p. 44, pi. v. 



figs. 10, 11, pi. vi. figs. 1-4, pi. vii. figs. 1, 8, pi. viii. fig. 4, pi. B. 



figs. 6, 7, 10, 13, 14. 

 1860. Asterolepis ornata, E. von Eichwald, Leth. Rossica, vol. i. p. 1508 



pi. lvi. fig. 1. 



Type. Detached dermal plates ; University of St. Petersburg. 



The type species. Anterior median dorsal plate not carinated 

 longitudinally, its anterior extremity almost as broad as the poste- 

 rior. Unworn superficial tubercles with prominently stellate bases, 

 irregularly arranged, and sometimes fused together; outer margin 

 of pectoral appendages acute and coarsely denticulated. 



Form. § Loc. Devonian : Baltic Provinces and Government of 

 Novgorod, Russia. 



The following specimens are detached plates from the neighbour- 

 hood of Dorpat, and, unless otherwise stated, were obtained by 

 purchase, 1868 : — 



41090 a. Premedian. 



1 Die Placodermen des devoniscben Systems (1857), p. 44. 



2 Geol. Mag. [3] vol. v. (1888), p. 508 ; also Ann. Mag. Nat. Hist. [6] vol. ii. 

 (1888), p. 492. 



