Linnean Transactions. 563 



to Mr. Hogg's observations, by one or two very minute shells, 

 which proved, on being hatched, to be the young of the lividNerite 

 of English CoUectorSjwhich, in conformity vrith their usual practice, 

 has been referred in the present paper to the Nerita glaucina. 

 The Nerita glaucina of the writers on British Conchology, is, how- 

 ever, certainly not that of Linnaeus, but is probably the shell 

 described by Lamarck under the name of Natica moniliferaj 

 while its variety, as it has been termed, which is the shell exa- 

 mined by Mr. H. and figured in the illustrative plate, appears to 

 be the N. collaria of the same authour. When sufficiently grown, 

 the young animal forces its way through the under surface of the 

 agglutinated sand, which forms the substance under examination, 

 leaving a small opening into the cell which it has quitted. From 

 these circumstances, Mr. Hogg concludes, that it is " evident that 

 it cannot be referred to the genus Flustra, but is rather to be con- 

 sidered as the matrix of Nerita glaucina, [of the English writers,] 

 in which the embryo shells are retained and preserved until they 

 have arrived at sufficient growth to obtain nourishment for them- 

 selves, and to support an independent existence." The figures of 

 this production, of the minute shells contained therein (magnified), 

 and of the young of that variety of N. glaucina, as it is termed, 

 which has been alluded to above, appear strongly to support these 

 results. 



The *' Description of a new species of Onchidium; by the Rev. 

 Lansdown Guilding," comprises an enumeration and distribution 

 of the species previously described of this singular and interesting 

 genus of Mollusca, which it is however unnecessary to quote ; 

 since, founded on external characters alone, it by no means ac- 

 cords with the arrangement recently proposed by De Blainville, 

 in the Dictionnaire des Sciences Naturelles, upon truly natural 

 principles. With this arrangement, Mr, Guilding could not have 

 been acquainted at the time of writing the present paper, or, ready 

 as he is at all times to adopt those improvements which the pro- 

 gress of natural science is daily making, he would, we entertain no 

 doubt, have agreed with that excellent Naturalist, in confining 

 the true Onchidia to the semi-aquatic fresh-water species, and 

 placing them near Limax, while the maritime ones are referred to 



