416 



J. W. DAVIS ON THE FISH-REMAINS OE 



the land ; of the fishes, the Sharks and some of the Ganoids 

 frequented the shallow waters, probably in search of food. That 

 they did so in large numbers, and spent considerable time there, is 

 amply proved by the large number of coprolites. 



Microscopical sections of the coprolites exhibit abundant evidence 

 that the food of the Fishes or Saurians to which they owe their 

 origin consisted of smaller fishes — fragments of bone, teeth, and 

 other similar objects belonging to smaller or more slightly armed 

 species of fish being found in larger proportions than any thing else 

 with structure. 



Hybodus austiensis, Davis. (Plate XXII. fig. 1.) 



In the third volume of the ' Poissons Fossiles ' M. Agassiz described 

 a spine of Hybodus, of which there were several specimens in the 

 cabinets of Lord Enniskillen and Sir P. Egerton, and in the museums 

 at Oxford andBristol ; and an example is figured from the latter, which 

 is about 6 inches in length. The spine is described as being round 

 (that is, the sides are not so much compressed) ; and the ribs are 

 more prominent, with deeper grooves between than in any other 

 species described. The ribs do not anastomose, but run parallel to 

 the anterior portion of the spine, and disappear along the posterior 

 margin. There is a large cavity along the posterior surface ; and the 

 base of the spine is large proportionally to the remainder. The 

 examples seen by M. Agassiz did not exhibit any traces of den- 

 ticles sufficiently well preserved to enable him to describe them. 

 Dr. Buckland and Sir Henry de la Beche knew the spine, and had 

 previously considered it a variety of their Ichthyodorulites dorsetiensis 

 { — Hybodus reticulatus, Agassiz) found at Lyme Regis. M. Agassiz 

 further remarks that H. minor is not a small spine when compared 

 with others he had described ; but, at the same time, the spines 

 found at Aust Cliff are not of large size, and are very different from 

 the great spines found in the Lias at Lyme Regis. The teeth 

 accompanying the spines are also different from those found at Lyme 

 Regis ; and altogether the differences are so great as to necessitate 

 the institution of a new genus. 



Since M. Agassiz wrote his great work, many fossil spines of 

 Hybodus have been found in the Rhsetic beds of Aust ; and the 

 collection at the Bristol Museum contains specimens which very 

 nearly approach the sizes attained by the fine examples of Hybodus 

 reticulatus and formosus of the Lias of Dorset. One of the largest 

 examples would measure, when perfect, 13 inches in length, and 

 fully an inch and a quarter in greatest diameter. The base pre- 

 sents the usual fibrous structure ; it has been deeply and strongly 

 implanted in the flesh. There is a large orifice or groove opening to 

 the back of the spine at its base, and afterwards continued as an 

 internal cavity towards the apex. The width of this orifice, from 

 back to front, is about double that between the sides of the spine. 

 The line dividing the base from the exposed portion extends with 

 a convex curve from the anterior to the posterior portion of the 

 spine, the convexity being towards the base. The anterior and 



