The Anatomy of Chlaynydoselachus 495 



to those of Cladodus, and went so far as to say that ''Chlamydoselachus is a cladodont." 

 In the present paper (p. 349) I have compared the teeth of the frilled shark with those of 

 two cladodonts, Cladoselache and Cladodus, and two hybodonts, Ctenacanthus and 

 Hyhodus (Text'figures 17, 18, 19, 20, on p. 348). The resemblance between the teeth of 

 Chlamydoselachus and the cladodonts is indeed striking, but the paleontological history 

 of Chlamydoselachus goes back no further than the Tertiary, while the cladodonts are 

 generally considered to be extinct since the Carboniferous. The teeth of hybodonts are 

 more generalised and variable; nevertheless, out of such structures, teeth like those of 

 Chlamydoselachus might readily have been evolved. The presence, in the hybodonts, 

 of a large spine at the anterior border of each dorsal fin does not exclude this family from 

 relationship with the Chlamydoselachidae. In the Spinacidae, some genera possess 

 spines similarly located, while other genera lack them. 



Throughout this article I have recorded and emphasized the great variability of 

 Chlamydoselachus in most of its structures. The significance of this variability is not 

 self'evident. ''As a paleontologist knows . . . variability is a special characteristic of 

 the struggling end of a disappearing race quite as frequently as it is a mark of the begin' 

 ning of a new race" (Woodward, 1933). There are reasons why, in the case of Chlamy- 

 doselachus, one may favor the former interpretation. The frilled shark has been taken 

 only in Japanese waters and off the western coast of Europe. If it were a new species, 

 one would not expect it to occur in waters so widely separated, particularly since it is 

 not gifted with extraordinary powers of locomotion. Since it is quite rare even in these 

 restricted localities, it seems to have a precarious hold on existence. It may be significant, 

 in this connection, that Chlamydoselachus anguineus is somewhat isolated in its systematic 

 position. The genus stands far enough from the Notidanidae to be placed in a separate 

 family, the Chlamydoselachidae, containing no other genera. There are no other species 

 save the fossil C. lawleyi and C. tohleri, both known only by their teeth (Text'figures 

 15 and 16, p. 348), and one may question whether the latter really belongs to the genus 

 Chlamydoselachus. The frilled shark appears to be a form that has long been differenti' 

 ated in adaptation for a particular habitat and mode of life, in which it has not been 

 altogether successful since it now seems to be facing extinction. 



My outstanding impression of the frilled shark is that it presents a strange assem' 

 blage of characters ranging from very primitive to highly differentiated. In this, it is 

 comparable to Chimaera, though the latter is specialized in a decidedly different way. 

 Chlamydoselachus is a deep'sea adaptation of some rather ancient type of shark, and is 

 now waging a losing battle in the struggle for existence.^ 



'Since writing these pages I have found in Deinega's (1925) English abstract of his Russian text the following statement: ""We 

 may still consider Chlamydoselachus as one of the most ancient representatives of the vertebrates, having survived to our day and now 

 undergoing extinaion" (italics mine). I do not know of any other author who has expressed the view that Chlamydoselachus is threaten' 

 ed with extinction. In my opinion, Chlamydoselachus is not '"one of the most ancient representatives of the vertebrates." It is, 

 however, one of the most primitive of existing sharks, 



