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burrow ; and having completely concealed itself, is foon found to hnv 

 turned within the tube. Mr. Osier describes the manner in which 

 this motion is effected by reference to an annexed drawing. 



The Spatangus buries itself chiefly by the action of its bristles, 

 while the long dorsal spines prevent the sand from closing entirely, 

 and preserve a small round hole, by which water is admitted to the 

 animal, and which marks its situation. 



The author next describes the burrowing of bivalves. The animal 

 projects the foot into the sand, and then gives a circular motion to 

 the shell, sinking at every stroke till nothing but the extremity of 

 the syphon can be perceived above the sand. This motion is effected 

 by two appropriate pairs of muscles arising from the shell, and in- 

 serted into the foot, the position and actions of which are explained 

 by reference to a drawing. The locomotive bivalves travel by a series 

 of motions similar to those of burrowing, as seen in the Venus gal- 

 lina, the Anodonta cygneea, &c. The Buccinum undatum, though not 

 habitually residing under the sand, is so often observed to bury itself 

 as to come within the author's arrangement : as in the bivalves, its 

 foot is the instrument of penetration, and, like them, it can distend 

 that organ to nearly the size of the shell ; the author describes its 

 anatomy by the help of annexed drawings. He also enters into a 

 detailed account of the peculiarities of structure of the Pholas, which 

 has two methods of boring. The first is almost exclusively employed 

 by the young animal ; it fixes itself by the foot, and having raised 

 itself almostperpendicularly, executes a succession of rotatory motions; 

 but when the animal is older, the foot being attached as before, it 

 brings the anterior points of the shell so as to press its operative part 

 against the bottom of the hole, and then the dorsal margins of the 

 valves are brought into contact, so that the rasp-like portions scrape 

 over the substance on which they press. In the Teredo, the pecu- 

 liarities of structure observed in the Pholas exist in an equally marked 

 degree. 



Mr. Osier next describes four species of Lithophagi, of which the 

 Saxicava rugosa is so abundant at Swansea, as to induce him to take 

 it as the type of the family. Its general structure resembles that of 

 the burrowing bivalves, but it does not admit of boring by any ro- 

 tatory motion ; and several other facts show that the shell is not the 

 instrument by which it penetrates hard substances, such, for instance, 

 as the absence of any arrangement of muscles for the purpose, and it 

 being able to penetrate certain substances only, all of which are of a 

 calcareous nature. Hence the author concludes, that the perforating 

 power of the Lithophagi is referrible to chemical rather than to mecha- 

 nical causes; and he refers it to some peculiar secretion which the ani- 

 mal forms, and which readily destroys carbonate of lime, whilst sili- 

 ceous and argillaceous stones resist its action. In conclusion Mr. Osier 

 remarks, that he has made many experiments with a view to detect 

 the nature of the solvent : he shows that it is not of an acid nature ; 

 nor has he been able to detect any peculiar soluble compound of 

 lime in portions of water, in which many Saxicavw hud been con- 



