60 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 37. 



behind the one in function. Newberry ^ states that the worn spine 

 is succeeded by another from behind. Jsekel ^ writes that usually one 

 finds in front of the base of an old spine the germ of a new one. 

 In a specimen of Rhinoptera honasus in the U. S. National Museum 

 there is found a very small spine, loosely attached, in front of the 

 one in function. In the German edition of Giinther's Study of 

 Fishes, translated by Hayek (p. 23G), is a figure of the tail of a 

 Myl'tohatis bearing two spines, the smaller of which is in front of 

 the larger one. Storer,<" speaking of Mijliohatis aeuta^ states that the 

 smaller spine is in front of the larger. It appears, therefore, that 

 in the Myliobatida^ the new spine comes up in front of the older 

 ones. On the other hand, Mr. B. A. Bean, of the U. S. National 

 Museum, has shown me a specimen of Urolophus jamaicensis and one 

 of an undetermined species of Twninra in which a considerably 

 smaller spine is behind the functional one; from which fact it may 

 probably be inferred that in the Dasyatida* the new spine arises 

 behind the one in function. 



It appears to the writer, therefore, that the objects called Edestus.^ 

 Lissoprion, Helicoprion, etc., may for the present be most easily dis- 

 l^osed of by supposing that some ancient elasmobranchs developed 

 in front of a median dorsal fin, or in place of it, not a single spine, 

 but a succession of them. The new compressed spine, serrated in 

 front and behind, arose in front of the older ones. Nevertheless, the 

 root of the new spine became directed backward beneath and on each 

 side of the preceding one, so as partly to embrace it. At first prob- 

 ably the older spines were shed, but in time they began to cohere and 

 thus form a compound spine. In Edestus this was straight or slightly 

 bent. All of it, or nearly all, except the serrated teeth, was buried in 

 the flesh. As more and more elements were added, the organ became 

 more curved and finally in some species formed a spiral, which was 

 directed backward and the last turn of the shaft of which was ele- 

 vated enough to keep the teeth from cutting into the skin. Such a 

 weapon could be brought into action if only its possessor had dived 

 under its victim and brought the spine across its abdomen, thus dis- 

 emboweling it, a suggestion already made by Trautschold. It is in 

 this way, as Doctor Gill informs me, that Gasterosteus attacks its 

 enemies. 



If possibly these organs belonged in front of a dorsal fin, that of 

 Edestus might have had its shaft buried in the fleshy part of the 

 front of the fin and directed upward and backward. The spiral of 

 Helic'oprio7i may be supposed to have been coiled on one side of the 

 fin to which it belonged. The fin would have formed a partial sheath 

 for the spiral. 



« Paleoz. Fishes N. A., p. 224. 



*Sitz.-Ber. Naturfor. Freunde, Berlin, 1890, p. 124. 



" Fishes of Massachusetts, p. 270. 



