CLASSIFICATION OP DEVONIAN FISHES. 



5 



As has been seen, the angles of the scales of Gyroptychius are 

 apt to become rounded off, so as to present a transition from the 

 rhomboid to the cycloid contour, and, hence, it is less surprising than 

 'it seems at first sight, to tind fishes with eminently cycloid scales, 

 so similar, ia all the essential features of their organization, to 

 Glyptolcemus, Gyroptychius, and Glyptopomus, as imperatively to 

 demand a place near them in any natural arrangement« 



Holoptychius (Agassiz), for example, has a depressed head 

 (though deeper than that of Glyptoloemiis), and a conically 

 tapering caudal extremity ; the orbits are situated far forwards 

 and the gape extends far back. The frontal bones are distinct 

 from one another, and from the parietals, which last are large 

 and co-adapted, though quite distinct ; the occiput is covered in 

 by three bones, a median and two lateral ; there are two prin- 

 cipal and a number of lateral jugular plates, and there is no rhom- 

 boidal median jugular plate interposed between the principal 

 jugulars. Some of the teeth are larger than the others, and longi- 

 tudinally striated at their bases. The paired fins are very acutely 

 lobate, and there are two dorsal fins placed in the posterior half of 

 the body. The ventral fins are situated under the first dorsal, and 

 are succeeded by a single anal. 



EiG. 5. 



Thus far, the reader who compares this description with that of 

 Glyptolcemus already given, will find the two essentially identical 

 But the tail of Holoptychius differs from that of Glyptolcemus, in 

 that it is little more than semi-rhomboidal, the upper moiety 

 being far less developed than the lower,^ and the scales are. 



* In my restoration ot Holoptychius (Dr. Anderson's " Dura Den," p. 69) I have repre- 

 sented the fish with a diphycercal tail ; but I am now prepared to admit that the evidence 

 on which I rested this conclusion was not trustworthy, and that Sir Philip Egerton's 

 view of the case is in all probability correct. However, I must say, that I have never yet 

 seen a Holoptychius with its caudal extremity in a perfectly satisfactory state of pre- 

 servation. 



