A SUMMER RAMBLE AMONG THE HEBRIDES. 221 



isting species, that John Stewart and Alister at once chal- 

 lenged them as smurslin, the Hebridean name for a well- 

 known shell in these parts, the Mya truncata. The remains 

 of fishes, chiefly Ganoid scales and the teeth of Placoids, 

 lie scattered among the shells in amazing abundance. On 

 the surface of a single fragment, about nine inches by five, 

 which I detached from one of the beds, and which now lies 

 before me, I reckon no fewer than twenty-five teeth, and 

 twenty-two on the area of another. They are of very various 

 forms, some of them squat and round, like ill-formed small 

 shot, others spiky and sharp, not unlike flooring nails, some 

 straight as needles, some bent like the beak of a hawk, 

 some, like the palatal teeth of the Acrodus of the Lias, re- 

 semble small leeches ; some, bearing a series of points ranged 

 on a common base, like masts on the hull of a vessel, the 

 tallest in the centre, belong to the genus Hybodus. There 

 is a palpable approximation in the teeth of the leech-like form 

 to the teeth with the numerous points. Some of the speci- 

 mens show the same plicated structure common to both ; and 

 on some of the leech backs, if I may so speak, there are 

 protuberant knobs, that indicate the places of the spiky points 

 on the hybodent teeth. I have got three of each kind slit 

 up by Mr George Sanderson, and the internal structure ap- 

 pears to be the same. A dense body of bone is traversed by 

 what seem innumerable roots, resembling those of woody 

 shrubs laid bare along the sides of some forest stream. Each 

 internal opening sends off on every side its myriads of close- 

 laid filaments : and nowhere do they lie so thickly as in the line 

 of the enamel, forming, from the regularity with which they 

 are arranged, a sort of framing to the whole section. It is 

 probable that the Hybodus, a genus of shark which became 

 extinct some time about the beginning of the chalk, united, 

 like the shark of Port Jackson, a crushing apparatus of palatal 

 teeth to its lines of cutting ones. Among the other remains 



