494 Bashford Dean Meinonal Volume 



the anterior border of the dorsal fin, resembling in torm and arrangement the "fulcral 

 scales'' of the Actinopterygii. It is scarcely necessary to add that these resemblances to 

 higher vertebrates have no phylogenetic significance. 



The expression "oldest Kving type of vertebrate'" used by Garman (1884.3 and 

 1884.4) and by GiU (1884.1 and 1884.2) v.nth reference to Chlamydoselachus, quite ignores 

 the cyclostomes. While the cyclostomes are in some respects degenerate, in others 

 highly organized, they retain, to a greater degree than any other vertebrates, the funda- 

 mental chordate structures. The view that skeletal degeneration has been a major trend 

 in fish history has its Hmitations, particularly when one considers the endoskeleton rather 

 than the external armor. Cartilaginous, calcified and bony vertebral centra develop 

 largely at the expense of the notochord, and it seems unlikely that degeneration of the 

 harder structures would result in the notochord being restored to its primitive condition 

 as an effective organ in the adult. In Cyclostomata, as in Holocephali, the notochord is 

 unimpaired. The ammocoetes larva of the lamprey Hnks this form v.'ith the lower chor- 

 dates rather than with the fishes. If phylogeny be defined as the succession of adult 

 forms in the line of evolution, this latter evidence is not admissible, but if organisms are 

 genetically related in the adult stage, then they must be related at all stages of their 

 development. The cyclostomes have long been regarded as the lowest group of Hving 

 vertebrates (crania tes), and the e\'idence in support of this vie^w should not be lightly 

 set aside. 



The very interesting question of the relationship ot Chlamydoselachus to fossil 

 forms is one that I am quite willing to leave to paleontologists. Such studies must remain 

 under the handicap that, m fossils, little knowledge is available concerning organs that 

 are quite as important as the more enduring skeleton. Since the "hard parts" of Chlamy- 

 doselachus, upon which we must depend for comparison w-nth fossils, have long been 

 known, it can scarcely be expected that the present paper will add much that will be 

 of value to paleontologists. W^hat has been added concerning the "soft parts" serves 

 to confirm the generally accepted systematic relationship of Chlamydoselachus to the 

 notidanids ■w.^ithout, however, bringing them any nearer together. WTiile Chlamydo- 

 selachus and the notidanids must be assigned to different families, the relationship is 

 closer than that between Chlamydoselachus and any other existing sharks. In this con- 

 nection the following quotation from Woodward (1921) seems pertinent: 



The Hybodonts, which for the most part exhibit the primitive notochordal condition 

 unto, the Lower Cretaceous Period, are especially interesting because, w-hUe their dentition 

 and their general appearance resemble those of the existing Cestraciontidae, their skuU is 

 very different and more closely agrees with that of the Notidanidae. They are indeed a 

 generalized group from which several later families appear to have arisen, and they are the 

 dominant sharks of the Jurassic and early Cretaceous periods. 



Pre\'ious discussions of the affinities of the frilled shark to fossil forms have been 

 re\T.ewed at length by Gudger and Smith (1933j. Garman (1885.2) was particularly 

 impressed by the resemblance of the teeth of Chlamydoselachus (Text-figure 7, P- 344) 



