462 PETRIFIED SHELLS. 



Of the remainder of the shells discovered in \ 

 petrified state in this neighbourhood, I shall do 

 little more then name some of the genera, as the* 

 limits of this work will not admit of elaborate dis- 

 cussion. Thdse which I shall name, will be ac- 

 cording to the subsequent arrangement. 



Solon or razor shelf, the species of which in the 

 limestone are numerous, as well as in the calcariou* 

 sandstone, in which we often see large specimens 

 of the solon silqua. 



Mytilus, Muscle. Of this genus the mytilus, litho- 

 phagus, or stone eater, which like the pholas, biuv 

 rows in rocks, and often in corals is found imbbeded 

 in the oolite at Malton and other places. The 

 muscle edulis or common muscle is very plentiful 

 in the same rock. The mya, gaper, is also plentiful. 



Donax, Wedgeshett, is another produced in the. 

 limestone rock ; also a shell of the douax family, 

 called plagiostoma or wrymouth, which is different 

 from the other species of that genus, as well as thet 

 plagiostoma rigida. 



Trigonia which is somewhat akin to the plagi- 

 ostoma, as it is also to the Venus, the Area, the 

 Mytilus and the Tilina. 



Some species of the Triogonia have been found 

 in the oolite and calcarious sandstone, near Kirkby- 

 Moorside, which Mr. Young calls Trigonia clavel- 

 lata, which from its shape appears to be akin to 

 the mytilus or muscle family. I have a mass or 

 shells of this description, of a very considerable; 

 size, imbedded in a matrix of oolitic- limestone, 

 which I found in Catterbeck in deepdale ; the 

 stratum containing them forms the bed of the beck^ 

 and by the constant action of the water on them, 

 the stony matter is partly washed out from the con- 

 cavity of the valves so as to make the edges of them 

 appear in their natural state. The water after heavy 

 rains running down the beck in a strong current, 

 sometimes loosens the rock beneath, and washes up 

 masses of these shells in the limestone of amazing 

 size. These shells when in their more perfect state, 

 are handsomely studded with tubercles disposed iix 

 rows. 



