M. R. Storms on the Adhesive Disk of Echeneis. 73 



tion of the spines is frequently observed among fishes, i. e. 

 Nauc7-ates, Elacate, &c. 



A comparison between a pair of pectinated laraelteand the 

 base of a spinous ray confirms this opinion. In both analo- 

 gous processes situated on the same side (if we suppose the 

 spinous ray bent down) can be seen, and between the two 

 himellffi, when they are joined, a hole or notch is observed 

 corresponding to that in the base of the spinous ray. 



111. 



Where was the Disk foemed ? 



This question, although it has not, so far as I know, been 

 discussed by naturalists, is not devoid of interest. Three 

 suppositions are possible : — 



1. The disk was formed in situ from a primitive fin ; 



2. Spinous rays migrated to the extremity of the snout, 



there to be transformed into a disk ; 



3. The disk was formed on the dorsal_ region, and then 



migrated gradually to its actual position. 



1. The Jirst supposition is very improbable, for in all 

 Teleosteans, and especially the Acanthopterygians, whenthe 

 dorsal extends to the extremity of the head it does so in a 

 secondary way (Pediculati, Pleuronectida3) . Moreover all 

 the nerves and blood-vessels for the disk come from the 

 cervical region *. 



2. The second hypothesis also seems improbable, tor it 

 supposes that a dorsal fin, more or less normally constituted, 

 migrated to the extremity of the head, a secondary position 

 for a dorsal fin rarely observed among fishes, and that this 

 migration had another cause than that of the transformation 

 of the fin into an adhesive disk. 



3. Therefore the tfiird supposition appears to be the most 

 likely, i. e. that the disk was formed on the anterior dorsal 

 region and migrated, after it was used as a disk, towards the 

 extremity of the head. 



IV. 



Echeneis olabonensis. 



The recent discovery of a well-preserved fossil Echeneis in 

 the schists of Glaris t is of special interest for our present 



* G. Beck, loc. cit. p. 27. ^, 



t Dr A Wettstein, " Ueber die Fischfauiia des tertiaren G arnei- 



fechiefeiv-," Abhandlungeii der schweizerischen palaontologischeu Lreseli- 



schaft, vol. xiii. (188G). 



