206 A. Smith Woodward — On the Genus Not id anus. 



Gill l regards the Notidanidee and the Cestraciontidee as the sole 

 existing representatives of the first two. 



Notidamis is also remarkable for the persistence of the notochord. 

 One section of the genus (ITexanchus) exhibits this gelatinous rod 

 merely subdivided by transverse membranous septa, while the other 

 (Ueptanchus) has annular cartilages in the sheath which only show 

 traces of calcification in the region of the tail. 2 



As regards fins, the genus under consideration differs from other 

 Sharks (except Chlamydoselachas) in possessing only a single dorsal, 

 without spine, which is placed far back, partly opposite the anal. 

 The latter is well marked off from the caudal. The structure of 

 these locomotory appendages in Notidanus is also interesting, but 

 there is much difference of opinion as to the conclusions to be drawn 

 from them. Prof. Huxley has given reasons 3 for regarding the 

 pectorals as of a more primitive type than those of other living 

 Selachians and as most nearly related to the so-called " archiptery- 

 gium" of Ceratodus ; while Prof. Mivart 4 is led to dissent entirely 

 from this interpretation, and to look upon it as nothing more than 

 " an ingenious speculation." The latter has also shown (loc. cit.) 

 how the basal cartilages of the dorsal and ventral fins, and, to a less 

 extent, those of the anal, have become fused together into a nearly 

 continuous mass, — a fact of considerable significance if, as seems 

 probable, the basals were a parallel series of thin cartilaginous bars 

 in -the earliest forms of fin. 



Another curious feature of Notidanus consists in its possession 

 of more than five gill-openings besides the spiracle, and in this 

 peculiarity it differs from all other living Sharks except the Ghlamy- 

 doselachus. Some of the species have six of these openings and 

 others seven ; and most ichthyologists prefer to regard each of these 

 types as constituting a distinct genus, the first named being termed 

 Hexanclius, and the second Ueptanchus or Heptranchias. Dr. Giin- 

 ther, 5 however, is inclined to admit no such separation, and as it is 

 quite impossible for paheontological purposes, it cannot be adopted 

 here. 



But the points to which the palaeontologist is naturally led to 

 devote most minute attention are those relating to the harder struc- 

 tures capable of preservation in the fossil state. And it fortunately 



1 In Jordan and Gilbert's " Synopsis of the Fishes of North America," Bull. U. 

 S. National Museum, No. 16 (1883), p. 967. 



2 See detailed descriptions of C. Hasse, " Das Natiirliche System der Elasmo- 

 branchier — Besonderer Theil" (1882), pp. 39-52, pis. vi. vii. 



3 Loc. cit. p. 50. 



4 St. G. Mivart, " Notes on the Fins of Elasmobranchs," Trans. Zool. Soc. 

 vol. x. (1879), p. 477. 



5 A. Giinther, "Catalogue of Fishes Brit. Mus." vol. viii. (1870), pp. 397-399. 



