126 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [May 18, 



constitute a second species. The small size, the uniformity of depth 

 of the greater part of the trunk, and the small expanse of the fins 

 are characters which can be relied upon ; for I have never found, in 

 any specimen I have examined, transitional features which could in- 

 dicate these as immature individuals of the larger species. This 

 subject, however, requires further consideration. 



Coitchodtts, new genus. — The materials on which this new generic 

 form is constituted are so scanty, that it should be kept in abeyance 

 until further evidence is obtained. 



Holoptychius. — I entirely agree in the propriety of restricting 

 this genus by the elimination of the larger Carboniferous species 

 under Prof. Owen's name Rhizoclus. It may be advisable here- 

 after, as our knowledge increases, to constitute this the type of a 

 family, as it differs in many respects from the Goelacanthi, and 

 especially in having an ossified vertebral column ; whereas in all the 

 Goelacanthi, from the Chalk downwards, the chorda dorsalis is per- 

 sistent. The description of the generic characters of Holoptychius 

 ascribes but one dorsal fin to this genus. It has undoubtedly two, 

 the anterior one considerably smaller than the other. 



Holoptychius Andeesoni. — The fine specimens recently obtained 

 from Dura Den, have satisfactorily shown that Holoptychius Ander- 

 soni and H.Flemingi can no longer be maintained as distinct species. 



HoLOPTYCHitrs pbinceps.- — -The detached scales upon which this 

 species is based do not differ more from those of Holoptychius gigan- 

 teus than do those upon which Agassiz founded the two Dura Den 

 species differ from each other. I do not think it can be upheld ; 

 certainly not without. further evidence. 



Holoptychius Sedgwicki. — This is a good and very distinct spe- 

 cies. It has for many years been labelled in my cabinet as new. 

 The anterior dorsal fin is distinctly seen in one of my specimens. 



Gyroptychius. — We are much indebted to Prof. M'Coy for the 

 definition of this new and fine genus of fossil fish, including two 

 well-marked species, Gyroptychius angustus and Gyroptychius cliplo- 

 pteroides. I differ, however, with him in classifying it among the 

 Goelacanthi, with which family it has no relation. The form and 

 structure of the fins and tail, and the mechanism of the scales, point 

 it out as a true member of the Saurodipteridoi, allied to Diplopterus 

 and Osteolepis, but differing from these genera in the surface- sculp- 

 ture of the integumental covering. In comparing this genus with 

 some other Goelacanthi, Prof. M'Coy alludes to Platygnathus of 

 Agassiz as being founded on the jaw of one fish and the tail of an- 

 other. On referring to the description of Platygnathus in the 

 ' Poissons Fossiles du Vieux Gres Kouge,' it will be seen that Prof. 

 Agassiz had great doubts on this subject. He says, " this genus 

 is only known to me by very incomplete fragments, of which it 

 is difficult to say if they even belong to the same genus." He 

 then proceeds to describe a specimen of Platygnathus Jamesoni as the 

 type of the genus. The recent discoveries at Diu*a Den have shown 

 that this is a good genus ; they also prove that Agassiz's doubts as 

 to the form from the Orkneys were valid. Hugh Miller considers 



