130 Proceedings of the Royal Physical Society. 



inches in length, and having their apices pointing towards 

 the mouth of the larger fish ; then a smaller one, probably- 

 one of the ventral spines ; lastly, there are here and there 

 exposed portions of the shagreen-like scaly covering, the 

 little quadrangular scales being mostly still in apposition. 



It might be suggested that here we have simply the re- 

 mains of two fishes accidentally squeezed together, one above 

 the other. But careful examination of the specimen, and 

 comparison of it with the " counterpart," indisputably demon- 

 strates that the Acanthodian remains are situated, not outside 

 the body of the Nematoptychius, but between its right and 

 left abdominal walls. For as the stone has so split, that 

 part of the substance of the large fish adheres to one slab, 

 and part to the other, the scales of the two sides of the body 

 can readily be distinguished, separated by a thin layer of 

 matrix. And looking at the slab on which the Neniatopty- 

 chius seems to lie on its right side, nothing can be clearer 

 than the position of the Acanthodian remains helow the left 

 and above the right body wall, and imbedded in the thin 

 separating layer of matrix to which I have alluded. More of 

 the Acanthodes could certainly be exhibited by careful work- 

 ing out, but so obstinately does the aforesaid layer of matrix 

 adhere to the delicate shagreen-like scales, save where it has 

 already split off naturally, that it is hardly possible to clear 

 it away without injury to the latter. Enough is otherwise 

 shown to demonstrate the relative position of the two fishes 

 to each other. 



In conclusion, two points may be noted in connection 

 with the specimen chronicled above : 



1. The swallowed fish must have been of very considerable 

 size in proportion to its captor, judging from the length of its 

 pectoral spines. This shows rather forcibly that the enor- 

 mously wide gape characteristic of the Palseoniscidse was not 

 bestowed in vain upon the larger species of the family. 



2. The Acanthodes was swallowed head foremost, as is 

 clearly shown by the position of its remains in the body of 

 the larger fish. This must necessarily have been the case, as 

 in any other position its formidable spines would have proved 

 an insuperable obstacle to its being swallowed at all. 



