74 M. R. Storms on the Adhesive Dish o/'Ecbeneis. 



purpose, as it most probably shows us an ancestral form of 

 the living types. We shall examine in tliis section whether 

 a study of this fossil throws any light on the three questions 

 treated of above, i. e. : — 



I. The morphological value of the disk as a whole. 



ir. The morphological value of the elements of the disk. 



III. Where was the disk formed? 



I. As to the first question, the disk of the fossil confirms 

 the opinion that it was formed of a dorsal fin, because 



1. It has a position more similar to that of a normal dor- 

 sal. The disk of Echeneis glaronensis is placed on the cervical 

 region, extending only onto the posterior part of the head, 

 instead of covering its whole surface up to the extremity of 

 the snout. 



But it might be objected that in the Glaris fossil 



a. The disk has been displaced backwards during fossiliza- 

 tion ; or 



/3. That the disk has lost all its anterior segments and 

 extended really as far forwards in the fossil as in the 

 living forms. 



a. To i\\Q first objection it maybe replied that all the other 

 elements of the skeleton of tiie fossil have been kept in their 

 real anatomical connexions, that they are even united together 

 by traces of skin, and therefore it is improbable that the disk 

 alone has changed its position. 



It is true that the roof of the skull has been displaced by 

 compression ; but even in this case it has not moved back- 

 wards or forwards, but has opened like the lid of a box, one 

 side of it being still in connexion with the other bones of the 

 head and shoulder-girdle. 



;S. To the second objection, as well as to the first, may be 

 replied that the frontal bones, by their pitted and striated 

 appearance, show that they were not buried under a layer of 

 muscles, but were near to the surface. Bones covered by 

 muscles, like those of the roof of the skull of the living 

 Echeneis, for instance, are smooth and have quite a different 

 appearance. 



2. By its narrowness it is also more like a normal dorsal 

 if, as Jias been shown above, the lamellge represent the en- 

 larged bases of the spinous rays and the superior interneurals 

 (baseost). 



II. Regarding the second qnestion, the morphological value 

 of the elements of the disk, attentive examination of the fine 

 figure in Dr. Wettstein's work does not furnish conclusive 

 evidence. It is even rather difficult to make out in it the 

 elements of the disk of a living Echeneis. Perhaps the study 



