Cope.] 5"4: [March 7, 



open above. The neurapophyses it is true unite, but at a distance above 

 the neural cord, and as attenuated rods. Third, "There is no vomer de- 

 veloped, but a triangular cartilaginous element pendent from the cranial 

 rostrum affords attachment for the palatine (read maxillary) element 

 anteriorly," etc. This element probably exists in the Colocephali and 

 similarly takes the place of the vomer, only differing in being ossified. 

 I have been accustomed to regard it as the homologue of the bone called 

 ethmoid in fishes. 



The character which distinguishes the Colocephali from the Enchely- 

 cephali, now that their maxillary and palatine structure are shown to be 

 essentially the same, is found in the hyoicl apparatus. In the Enchely- 

 cephali, the structure is as in ordinary fishes ; there is a glossohyal, and 

 there are basihyals, and axial branchihyals, and superior pharyngeals. In 

 the Colocephali all these elements are wanting, excepting the fourth supe- 

 rior pharyngeal, which has the form of an antero posteriorly placed den- 

 tigerous jaw, which opposes the lateral branchihyal of the fifth arch or, 

 as it is generally called, the inferior pharyngeal. It is evident that the 

 Eurypharyngidse are more similar to the Colocephali than to any other 

 order in this respect also, but the description of these parts is not yet suffi- 

 ciently detailed to enable me to determine what difference there may be 

 in this respect, if any. The mobility of the quadrate bone on the hyo- 

 mandibular cannot be regarded as of great systematic significance, although 

 it is doubtless important in the economy of the fish. 



It is then evident that the EurypharyngidiE belong very near to, if not 

 within, the order Colocephali. Towards the end of their description, 

 Messrs. Gill and Ryder (p. 270), recognize this relationship, but deny that 

 it indicates that this family is "from the same primitive stock as the 

 Mursenids." I incline to the belief that it is the ultimate result of the 

 line of development of which the Anguillklae form one of the first terms, 

 and the Muraenidse a later and more specialized one. 



It is therefore clear that the point of relationship of the Ichthyotomi to 

 the true fishes is not to be found in the Eurypbaryngidae or the Colo- 

 cephali. 



In the following point Didymodus resembles Polypterus. The fossa 

 above described as on each side of the basioccipital, is found in Polypterus. 

 There it serves as a place ol insertion of a strong ligament on each side, 

 which is attached externally to the epiclavicle, and serves to hold the 

 scapular arch in its place. A similar structure exists in the Siluirdae, 

 where the ligaments are ossified. It suggests for Didymodus a scapular 

 arch suspended more anteriorly than in sharks, possibly even to the skull. 



The genealogy of the fishes will then be as follows, first, however, it 

 is to be understood that in asserting the derivations of one group from 

 another, I mean that in accordance with the rule which I have termed 

 "the doctrine of the unspecialized," the later type in each case is the 

 descendant of the primitive and not the later sub-form of its predecessor. 

 In this way is to be explained the apparent anomaly of regarding the 



