86 report — 1842. 



The form of the disc of the head of the Cephalaspides, which has the appear- 

 ance of a large crescent, and their more numerous but very elevated scales, 

 resembling the transverse articulations of the body, explain how it was possi- 

 ble to see in these fishes Trilobites of a particular genus. Lastly, the winged 

 appendages of the sides of the head of Pterichthys, as moveable as fins, have 

 easily °-iven rise to the variety of opinions concerning the true affinities of these 

 singular creatures, and has caused them to be taken at one time for gigantic 

 Coleoptera, at another for Crustacea or small marine Tortoises ; so little do 

 the types of the classes appear fixed in certain respects at those remote times. 

 Another singularity of these genera is the association to the bony plates of 

 the head of a vertebral appendage, which is far from having acquired the 

 . same solidity, but appears, on the contrary, to have remained fibro-cartilagi- 

 nous during the whole life of the animal, resembling in this respect the ske- 

 leton of the Sturgeon. 



It would be difficult to find among recent fishes types presenting any direct 

 analogy with the genera Pterichthys, Coccosteus, and Cephalaspis ; it is only 

 from afar that they can be compared to some abnormal genera of our epoch. 

 Thus the Sturgeons, (and especially Loricaria and Callichthys), offer but a 

 slight analogy with the Cephalaspis in their shielded head, and in the bony 

 plates of their flanks ; the bony shields ornamented with scidptures and re- 

 gular granulations, which protect the head of the Trigla, of the Peristediones, 

 and of the Dactylopteri, in a slight degree call to mind what is seen in the 

 "•enus Coccosteus, without however the analogy being perfect ; the structure 

 of the throat and the remainder of the skeleton are very different ; and lastly, 

 I find it impossible directly to compare those moveable appendages of the 

 sides of the head of Pterichthys to anything observable in fishes of the present 

 period. Perhaps they have some relation with the moveable sub-orbitals of 

 the Acanthopsis of the family of the Cyprinoids ; perhaps they might likewise 

 be compared to the prolongations of the prreoperculum o£ certain Trighc, 

 and in particular of the genus Cephalacanthus ; but I have found it impossi- 

 ble as yet to determine precisely with what bone of the head these extraor- 

 dinary appendages must be considered parallel. As to the less solid nature of 

 the vertebral column of these fishes, they have it in common with the greater 

 part of the species of the older rocks. The analogy which they offer on the 

 one hand in form with the dorsal cord of the embryo of fishes, together 

 with the inferior position of their mouth, which is equally met with in the 

 embryos, and, on the other hand, the distant resemblance of these fishes to 

 certain types of reptiles, present the most curious assemblage of characters 

 that can possibly be conceived. 



A third group of fishes belonging to this formation comprises those genera 

 whose vertical fins are double on the back and under the tail, and which 

 approach very near to the caudal. These are the genera Dipterm, Osteo- 

 lepis, Diploptervs, and Glyptolepis, which differ from one another by the 

 form of their scales and their dentition. 



And lastly, it seems to me necessary to regard as a fourth group of this 

 order the genera which are characterized by large conical teeth situated 

 on the margin of the jaws, between which are alternately smaller, and in- 

 deed very small ones in form of a brush ; such are the genera Holoptychms 

 and Platygnathus, and the genus recently established by Mr. Owen under 

 the name of Dendrodus, and respecting which this learned anatomist has 

 o-iven some exceedingly interesting microscopical details. These were evi- 

 dently the Pirates of their day ; but it would be difficult to determine pre- 

 cisely their size, for the very simple reason that nowhere have any portions 

 of their body of any considerable size been discovered assembled together. 



