Linruean Society. 181 



ater : lichenivora ; rufus ; mutabilis : tenax : and agrestis. The belly 

 of the snail being perfectly smooth, there are no appendages to do 

 the office of feet 5 and the whole of the body moves at once, and not 

 in parts successively. By placing the animal on a piece of glass, 

 Mr. Main was enabled to observe a muscular motion ; but this, in- 

 stead of being from head to tail, was directly the reverse, so that the 

 animal's motion cannot be caused by impulses in the direction of its 

 progress. He gives, in conclusion, two conjectures as to the cause 

 of the animal's motion j namely, 1st, that the body is moved forward 

 by the retromissive discharge of slime, which being emitted simul- 

 taneously from every part of the under surface, he conceives may ex- 

 ercise a force adequate to the propelling of the animal s — or 2ndly, 

 from its power of forming its lower surface into segments of circles 

 along the whole of its length j and thus by assuming a vertical ver- 

 micular action on the plane of the sustaining surface, impelling the 

 body forward by alternate contraction and expansion. 



As dry air deprives the animal of motion, Mr. Main is inclined to 

 consider the first surmise the more probable. 



Read an extract from a letter from Dr. Rigby to Mr.R. Taylor, dated 

 Berlin, on the ova of the Hirudo medlcinalis •" with some specimens. 



Read also "An account of Margarodes, a new genus of insects 

 found in ihe neighbourhood of Ants' Nests ; by the Rev. Lansdown 

 Guilding, B.A., F.L.S. &c." Mr. Guilding, after quoting Dr. Nugent 

 (Geol. Trans, vol. v. p. 463), who states that the ground pearl (im- 

 properly supposed to be fossil) is found in prodigious quantity in the 

 furrows of the land in Antigua when newly turned up, and suggests 

 that it may be the production of an insect, informs us that he has 

 succeeded, by watching some that he preserved in moist marl, in de- 

 tecting the insect which issued from them. He conceives it to be a 

 parasite on the ants, whose formidable numbers in the dry islands, 

 they are calculated to keep down. The entire want of a mouth is 

 remarkable in this new insect, the food being absorbed by tubes in 

 the fore claws. It also possesses the extraordinary power of throw- 

 ing out long filaments, when in dry situations, supposed to be for 

 preserving itself by obtaining moisture. Its scales effervesce and 

 disappear in nitric and muriatic acid ; sulphuric turns them black 3 

 and vinegar slowly decomposes them. In flame they burn like horn. 

 Mr. G. is uncertain at present what station is to be assigned to this 

 insect. 



Dec. 18. — Three new species of Land Tortoise were exhibited by 

 Mr. Bell : — Testudo pardalis, actinodes. and tentoria, descriptions of 

 which are given in the number of the Zoological Journal just pub- 

 lished. 



Read a portion of Dr. Hamilton's " Commentary on the Hortus 

 Malaharicus" 



Jan. 15, 1828. — Some specimens of lanthince were exhibited by 

 L. W. Dillwyn, Esq., washed ashore in July last in Oxwick bay near 

 Swansea, many of them picked up alive and yielding a beautiful 

 dye. Specimens of the Medusa Vellela and M. Navicula were found 

 with them. 



S 2 Read 



