402 



H. B. rOLLARD, 



Comparison. 



To compare the primordial cranium of Polypterus with that of 

 Selachians one has to make three obvious postulates: 



(1) That the perichoudrial bones be considered as non existent. 



(2) That the supracranial fontanelle be considered to have a 

 complete cartilaginous tegnien crauii of which only the 

 remains are now known. 



(3) That vertebral elements be considered as completely se- 

 parate. 



Granting these a most wonderful similarity will be seen to exist 

 between Polypterus and Selachians, with Chlamydoselachus and the 

 Notidanidae. The likeness may be noticed not only generally in the 

 (elongated) guitar shape but in many special points which it will be 

 necessary to take seriatim. 



The cartilage in Polypterus is, though extensive, not specially 

 massive therein agreeing rather with Chlamydoselachus than with the 

 Notidanidae. It is also fairly uniform in special tracts. 



In the occipital region the resemblance between the three types 

 is seen in the slope of the exoccipitals and in the low occipital crest 

 and also in the furrow leading to the vagus opening. There is no 

 parietal pit (Parietalgrube) in Polypterus for where it should occur 

 we find the great fontanelle. However attached to the parietals at the 

 point where it existed there is a little mass of tissue (unfortunately 

 too macerated in the sections to reveal its structure) which is pig- 

 mented and can be seen as a darker spot through the glassy bones. 

 Possibly this indicates where the ductus endolymphatici once opened. 

 Various foramina described by Gegenbaur in the Notidanidae nmst 

 be considered as uniting to form the large vagus foramen of Poly- 

 pterus. 



No less indicative of a genetic connection with the Notidanidae 

 is the protuberance of the saccular or vestibular wall with the relation 

 of the facial and glossopharyngeal nerves. The ridge on the pterotic 

 which serves for the attachment of the retractor hyoniandibularis and 

 leva tores arcuum is comparable with one present in Chlamydoselachus 

 leading in the latter to a considerable process termed pterotic by 

 Garman. The prominent process above is the epiotic of the same 

 author. 



In the orbital region the supraorbital band deserves special at- 

 tention. It corresponds to the outer rim of the orbital ledge of Se- 



