261 



like appearance, induced Lhwydd to give the name of Scapula litoralis to 

 this fossil. 



The comminuting surface of the first of these fossils, Plate XIX. 

 Fig. 16, is gently convex ; whilst that of the latter, Fig. 17, possesses a 

 correspondent degree of concavity. From this circumstance I am led to 

 suppose, that the former has been the lower part or tongue, and the 

 latter the upper part or palate, of perhaps the same species offish. 



Plate XIX. Fig. 14, is another fossil palate, of a different species. 

 This differs from the preceding species not only in the form of its plates, 

 but in its structure. The lateral substances are here plates, laying over 

 each other, like the tiles of a roof, ready to succeed, as the upper plates 

 are worn or broken away. The substance of the plates, in this speci- 

 men, when examined by a lens, are seen to be very different from that 

 of bone ; appearing, indeed, rather deserving a place between enamel 

 and horn : possessing, with a denseness of structure like that of the for- 

 mer substance, a small degree of the transparency observable in the 

 latter. 



Those bodies which are called by the quarry men petrified leeches, of 

 which one is figured Plate XIX. Fig. 15, and which are frequently found 

 in the lime-stone of Wiltshire and of Oxfordshire, were termed bv Da 



/ 



Costa Palatum Umax, or the slug-palate. These bodies are of an oblong 

 figure, and generally a little pointed towards their ends. Their colour is 

 of a dark brown, and they frequently possess a tolerable polish. On their 

 upper surface are innumerable fine and slightly undulating rugae, which 

 commence at the sides, and sometimes unite in a fine irregular line, 

 which passes longitudinally along the middle of this surface. The whole 

 appearance of this fossil very much resembles that of a leech or slug in a 

 contracted state. 



From these bodies having been found regularly disposed together, and 

 particular!}' from one instance mentioned by Mr. Walcot, in which 

 twenty-five of these oblong bodies were regularly placed in four rows, 

 there can be no doubt that they are not single palates ; but that many 



