SYSTEMATIC REVISION OF THE SUBORDER. 35 



Original description (taken from the Ann. and Mag. Nat. Hist.): "M. Roche, 

 director of the Iron Works at Igornay, to whom we are already indebted for several 

 discoveries of curious fossils, has just found, in the Permian, a new genus of reptile, 

 which he has presented to the Museum of Paris. The Igornay animal is the most 

 perfect of those which have hitherto been met with in the Primary formations of 

 France. I propose to name it Stereorachis dominans. 



" In Stereorachis the vertebrae present a striking contrast to those of the reptiles 

 of the same deposits. While in Actinodon and Enchyrosaurus the centra are composed 

 of a median part, or hypocentrum, and two pleurocentra not soldered together, in 

 Stereorachis the centra are in a single piece, which adheres to the neural arch ; the 

 vertebral column has therefore acquired more solidity, which has led me to invent the 

 name Stereorachis. It must, however, be noted that the centra of the vertebrae were 

 still extremely hollow; their anterior and posterior faces were so concave that they 

 formed two cones united end to end ; I would not even assert that there was not a 

 perforation establishing the continuity of the notochord. This is a condition analo- 

 gous to that of many fishes. 



"The new genus found by M. Roche presented another mark of superiority over 

 the reptiles that lived with it. Its humerus had a neuro-arterial canal in the distal part. 

 I had already called attention, in Enchyrosaurus., to the rudiments of the arch, indicating 

 a tendency to the formation of this canal ; in Stereorachis the fonnation is completed. 

 When we find that, besides the neuro-arterial canal, the humerus had the epitrochlea 

 and its epicon widened as in those animals in which the supinator and pronator muscles, 

 the extensor and flexor muscles, are greatly developed, we are led to think that the old 

 quadruped of Igornay had arms more perfectionated than those of existing species. 



^'■Stereorachis must have been a carnivorous animal of considerable size ; one of 

 its mandibles, although a little broken, measures 18 cm. The upper and lower jaws 

 are armed with conical teeth deeply immersed in the sockets ; their section is nearly 

 circular ; they are smooth externally, with a radiate structure in the interior ; the 

 front ones are stronger than the rest ; an inferior tooth has a crown 32 mm. high ; a 

 superior tooth, the j^oint of which is unfortunately broken, must have been at least 

 40 mm. There is an entosternum which recalls that of the Labyrinthodonts ; it is 

 very broad in its anterior third and narrowed behind ; its length is 15 cm. Beside it 

 there is a large nearly quadrilateral bony plate, 14 cm. long and 5 cm. broad ; I 

 suppose this to be the homologue of the coracoid and scapula. There is also a curved 

 bone which I believe to be the homologue of the great bone in fishes regarded by 

 Mr. Kitchen Parker as a clavicle (epistenutm of the Ganocephalus reptiles). I must 

 also notice long and arched ribs, formed by two pieces united end to end ; and hard, 

 brilliant, very fine, long, aciculate scales, as in Archegosaurus and Actinodon. 



"In some respects Stereorachis shows affinities with the Ganocephala and 

 Labyrinthodonts. In other respects it shows tendencies towards certain genera of the 

 Permian of Russia and the Trias of South Africa, upon which Professor Richard 

 Owen has made admirable investigations, and for which he has proposed the name 

 Thcriodonts. Perhaps it still more nearly approaches some North American animals, 

 such as Empedocles, Clepsydrops.,B.-aA Dimetrodon, ranged by Professor Cope in his group 

 Pelycosauria ; but at present I know no genus with which it could be identified." 



A more complete description of this form appeared in 1883 (93) with 

 figures. It was placed among the Stcgocephali in Zittel's Handbuch, but 

 later was referred by Lydekker to the family ClepsydropidcB in the order 



