ASTEROLEPIS. 71 



Astebolepis, Eichwald, 1840. 



Chelonichthys, Agassiz. (?) Actinolepis, Agassiz. 



Odontacanthus, Agassiz. (?) Nabcodes, Agassiz. 



Coccostetjs, Agassiz (pars). 



Generic Characters. — Median dorsal plate overlapping both the anterior and 

 posterior dorso-lateral plates. Arms shorter than the body-carapace; articular 

 plates of the upper arm scarcely meeting externally over the external marginal. 

 Post-median plate of the head large and broad, excluding the median occipital 

 from the margin of the orbit ; pre-median plate notched in front ; extra-lateral 

 plate loosely articulated with the rest of the cranial shield. External ornament 

 of plates consisting of raised tubercles with stellate bases, which may be some- 

 times confluent. Lateral line system on the head connected by two commissures, 

 a posterior one crossing the hinder part of the median occipital, and an anterior 

 crossing the pre-median plate in front of the orbit. Tail unknown. 



So far as is known, the characters of Asterolepis do not differ essentially from 

 those of Pterichthys except in the mode of articulation of the anterior median 

 dorsal plate, which in the latter genus is overlapped by the posterior dorso-lateral. 

 The tail is, however, unknown, owing to the disjointed condition in which its 

 remains have hitherto only occurred. 



History. — English readers who are acquainted only with popular works on 

 Geology and Palaeontology may be surprised to find that the Asterolepis here 

 described is not the " Asterolepis of Stromness," which in the middle of the century 

 attained celebrity through the writings of Hugh Miller. The latter is a huge 

 Coccostean, referable to the genus Homosteus of Asmuss, and having no affinity to 

 the original Asterolepis of Eichwald, which must retain its name by the inexor- 

 able law of priority. That such a state of confusion came to exist in the nomen- 

 clature of these fishes was entirely due to a mistake on the part of Agassiz, a 

 mistake which was for long years implicitly accepted in this country, owing to the 

 overwhelming authority of his name. 



The genus Asterolepis was established by Eichwald in 1840 x for certain isolated 

 plates from the Devonian of Russia, which proved to belong to an animal closely 

 allied to if not generically identical with that to which, from Scottish specimens of 

 entire fishes, Agassiz had about the same time given the name of Pterichthys, but 

 which was first described and figured by Hugh Miller a year later, 2 though the 



1 " Die Thier- und Pflanzen-reste des alten rothen Sandsteins und Bergkalks im Novgorodschen 

 G-ouvernement," ' Bull. Soc. St.-Petersbourg,' April, 1840. 



2 'The Old Red Sandstone, or New "Walks in an Old Field,' Edinburgh, 1841, pp. 49—53, 

 pis. i and ii. 



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