172 



HARDWICKE'S SCIENCE-GOSSIP. 



CHAPTERS ON FOSSIL SHARKS AND 

 RAYS. 



By Arthur Smith Woodward, 

 OF THE British Museum (Natural History). 



I. 



HOWEVER much care a palaeontologist may 

 bestow upon the naming and classifying of the 

 relics of animals with which he is concerned as a 

 student of fossils, it is at all times most difficult, and 

 cften impossible, for him to render his nomenclature 

 and arrangement of equal value to that of the 

 zoologist, who has complete animal structures to 

 guide his determinations. Although paleontology is 

 intimately connected with geology, and cannot well 

 be separated from it, it still bears a close relationship 

 to zoological science, and is, in fact, simply that 

 branch which attempts to unravel the characters of 

 the various faunas that have inhabited the earth 

 during the successive ages of the past. Nevertheless, 

 it requires but little thought to perceive that the 



patch of shagreen, or find a single spinous dermal 

 plate ; and occasionally we are delighted to meet 

 with a nearly complete mouth or head, or possibly 

 with all the hard parts of one individual, — either a 

 veritable "jumble," or else showing an outline of 

 the original fish. 



Such being the facts, therefoie, it is not in the 

 least surprising that the different parts of any one 

 true species should often have been described as 

 belonging to two or more species, or even to two or 

 more distinct genera ; at the present time, indeed, 

 there are very many forms of teeth and spines known 

 by names that are merely provisional, and when 

 their true relationships to each other have been de- 

 termined, it will still be extremely difficult to relegate 

 them to a correct place in classification. 



That it is necessary for paL^ontologists to employ a 

 provisional nomenclature in these puzzling instances, 

 will be admitted by all students of fossil remains ; 

 but, at the same time, the so-called specific and 

 generic distinctions ought not to be based upon 

 differences too trivial, and we can scarcely agree with 

 those who think it advisable to assign such small 



Fig. 99. — Pafeto-quadrato-mandibiilar arch (= jaws) 

 of Spinax (nat. size), s, suspensorium. 



Fig. 100. — Outline of Spinax (much reduced). — a, spiracle ; li^ V^, dorsal 

 fin-spines; c, giIl-openings|; d, mouth; e, nostrils ;y, eye. 



methods of grouping living animals must generally 

 differ greatly from those employed in the case of the 

 extinct forms, and consequently it is obvious that 

 palseontological species are nearly always distinct in 

 kind from zoological species. This ciicum.stance is 

 chiefly brougiit about, as is well known, through the 

 fragmentary nature of most fossilised organic remains ; 

 and the imperfection in materials is due to the fact, 

 that only the hard parts of animals have usually been 

 preserved, while the softer tissues — so important for 

 classificatory purposes — have almost always been 

 completely destroyed. 



Now, of all the groups of fossils, there is, perhaps, 

 none which exhibits more clearly the difficulties of a 

 palseontologist than that comprising the elcs of 

 sharks and rays. The larger kinds of the e fis' es are 

 very rarely met with unmutilated in any rocks, and 

 it is somewhat unusual, also, to find the sn.aller 

 species in any but an exceedingly fragmentary state. 

 Often, we discover a few teeth, or even only a single 

 one ; sometimes, there is nothing but a fin-spine ; 

 sometimes, we have a more or less incomplete ver- 

 tebral centrum, or, it may be, a short series of centra ; 

 at other times, we observe the faint indications of a 



limits to variations as has been frequently done, and 

 more particularly in recent years. 



In this short series of papers, it is proposed to give 

 an outline of the pala^ontological history of the 

 Selachian fishes, so far as it has been revealed 

 through scientific research up to the present time ; 

 and we shall attempt a zoological, rather than a 

 stratigraphical arrangement, although it will be almost 

 impossible to adhere strictly to either. 



But before proceeding with this paloeontological 

 sketch, it will be well, perhaps, in the first place, to 

 enter upon a few preliminary considerations, and take 

 a general glance at the sharks and rays as represented 

 in the living fauna of the globe. They are usually 

 grouped with Cliiniara and Callor/iynchus in an 

 order variously termed Elasmobranchii, Selachii, or 

 Chondropterygii, and this order is further divided 

 into the suborders of Plagiostomi and Holocephali, — 

 tlie former comprising the families with which we 

 are here concerned, and the latter the two Chimseroid 

 genera just mentioned. Both these divisions agree in 

 many important respects, and they are regarded by 

 most ichthyologists as forming quite a natural order ; 

 but others are inclined to make them much more in- 



