i54 



HARDWICKE'S SCIENCE-GOSSIP. 



and many failures will occur before a satisfactory 

 ■view will be obtained, unless singularly fortunate or 

 proficient. 



The teeth are of two distinct types, and associated 

 with them are other organs to which reference will 

 be made. The primary set are stout and admirably 

 formed for puncturing the skin of the victim selected. 

 They are five in number (dealing as heretofore with 

 one half of the mouth), each of these carries one 

 rather small point or denticle, and, in addition, they 

 are very finely serrated, three on one side only, the 

 two central ones on both sides, but it requires a high 

 power to see this distinctly. In this respect the 

 figure is slightly exaggerated for clearness' sake. 

 Immediately behind these teeth, and situated near to 

 their apex, is a set of short curved appendages, a 

 pair being allotted to each tooth. They 'are quite 

 opaque and uniform in thickness throughout. Their 

 use appears to be for maintaining hold while the 

 other instruments do the cutting and wounding. 

 Next follow a set of sabre or lancet-shaped teeth, 

 very fine at the points, and by the lightness of colour, 

 delicate in structure, but, nevertheless formidable in 

 number for the size of the mouth. These are the 

 organs for making an incision. When this has been 

 accomplished, the small hooks are inserted, and the 

 primary set soon completes the work. The margin of 

 the mouth is very thickly set with strong hairs, each 

 springing from a well-defined base, apparently capable 

 of movement. The integument is quite opaque, but 

 near the margin assumes a tesselated appearance, 

 the original cellular structure being preserved, the 

 cells are partly filled with pigment, thus leaving the 

 margins well defined. 



It will be observed there are no pseudo-trachea 

 present as in the Muscidas, and as these play an 

 important part in the collection and conveyance 

 of the food, their absence is fully provided for in the 

 organ I have attempted to describe. 



If these creatures are plagues when alive, to the 

 microscopist, they are in death doubly so, at least 

 with regard to their mouth organs. Small, hard, and 

 very brittle it is extremely difficult to obtain a 

 fairly representative mount, but patience and per- 

 severance will accomplish much. In this case it has 

 done a little to explain the wonderful contrivance 

 employed to replenish the larder of this little 

 creature. 



Slugs Biting. — It is stated by Rimmer that 

 Testacella will " bite savagely." I have never 

 succeeded in making it do so, but the other day on 

 handling a large black specimen of Arion ater the 

 animal at once seized one of the folds between the 

 fingers of the hand on which it was placed. The 

 rasping action could be distinctly felt, and after he 

 had been allowed to operate for about a minute the 

 skin was seen to be abraded. — W. Gain, Tuxford. 



CHAPTERS ONf FOSSIL SHARKS AND 

 RAYS. 



By Arthur Smith Woodward. 



V. 



SriNACID^E. 



THE Spiny Dog-fishes and their allies form a large 

 family whose palaeontological history appears 

 to begin with the deposition of the Lias. So far as is 

 known, Palccospinax, from the Lower Lias of Lyme 

 Regis, is the fore-runner of the race, and the earliest 

 example of a living genus is Spinax primavus, from 

 the Cretaceous rocks of Mount Lebanon. 



Exceedingly perfect specimens of Pahzospinax 

 have been discovered in the well-known Liassic fish- 

 beds of Lyme Regis, and by a study of these remains 

 Sir Philip Egerton has been able to elucidate the 

 structure of the genus ;* space, however, prevents us 

 from entering far into the anatomical details, and it 

 is only possible to glance at one or two of the most 

 prominent features. The ordinary length of the 

 shark being not much more than eighteen inches, the 

 teeth are very minute, and the use of a lens is 

 necessary to reveal their characteristics. They are 

 remarkably Hybodont in shape, but a great difference 

 exists between those of the upper and lower jaws, 

 and there is also considerable variation even in the 

 dentition of the same jaw ; fig. 101 represents a tooth 

 from the anterior part of the upper jaw, and fig. 102 

 a lower tooth of corresponding position. The dorsal 

 fin-spines (fig. 105, A, b) are likewise of small size, and 

 their external surface is smooth, exhibiting no 

 ornament except a few scattered tubercles and 

 indistinct lines of growth at the base of the exposed 

 portion : it is interesting to notice that the anterior 

 spine (a) is smaller, stouter, and more recurved than 

 the posterior (b) — the reverse of what occurs in 

 Hybodus and Acrodus. The slender body is covered 

 with fine shagreen, and the fins appear to have 

 possessed strong supporting rays of cartilage; and, 

 although the second dorsal fin almost corresponds in 

 position with that of Cestracion, there are indications 

 of the anal being merged with the caudal (according 

 to Egerton), and this is a special character of the 

 family now under consideration. 



The history of Drepanephorus affords a typical 

 example of the slow but steady progress of palaeon- 

 tological knowledge. In 1S22, some spines and 

 vertebrae from the Chalk of Lewes were referred by 

 Dr. Mantell to the Teleostean "File-fish," Balistcs. 

 In 1838, Frof. Agassiz showed that the fossils in. 

 question really belonged to a shark, and considered 

 them to indicate an extinct species of the living 

 genus, Spinax, which he designated S. major. 

 Twelve years later, Sir Philip Egerton described 



* Mem. Geol. Surv., Dec. XIII., 1872, PI. VII. ; see al-o 

 "Quart. Journ. Geol. Soc.," vol. xxix., 1873, p. 420; and 

 " Ann. and Mag. Nat. Hist.," [5], vol. vii., 1881, pp. 429-432. 



