Natural- Historical Collections. 65 
cient and modern anatomists, was endeavoured by the lecturer to be disproved, . 
and was declared by him to be contrary to daily observation and to common sense, 
The type, apparently, agreeably to which Nature (selecting, as seems usual, 
the most complex, ) had formed the generative organs, was hermaphroditical, and 
the organs being restricted to male and female, in those groups of animals whose 
functions and organization required that two individuals should constitute the 
species; but it was also shewn that the type existed in many animals, and 
that even in those species in which the sexes were most strikingly separated, the 
rudiments of all or of many of the organs, required by Nature to constitute the 
- original type, remained as evidence of her great plan. Finally, aberrations from 
regular structure, as regards the generative organs, hitherto described as herma- 
phrodites, lusus nature, monsters, ill-formed males or females, &¢. were reduced 
to the simple law of a return to the original type. 
We shall be careful to lay before our readers the whole of the inquiry, which, 
we understand, it is Dr. Knox’s intention first to submit to the Royal Society of 
‘Edinburgh, . 
Observations on Mr. Kenyon’s Paper on British Land and Fresh Water 
Shells. By CapTAIN THOMAS Brown, F.R.S.E. &c. &c.—in a Letter to 
the Editors. 
GENTLEMEN, 
I was in hopes that some person, better qualified than myself, would have 
given answers to Mr. Kenyon’s “‘ Remarks on British Land and Fresh Water 
Shelis,’” which appeared in the Fifth Number of ‘* Loudon’s Magazine of Natu- 
ral History,” page 424; but as no notice has been taken of that paper, I beg with 
deference to offer a few observations on it, and shall follow the order in which 
Mr. K. has given the species. 
Neritina virginea is a fresh water shell, very common in all the West India 
Tslands ; but it certainly has never been found alive in Great Britain or Ireland. 
I saw the shell described by Dr. Turton, as having been “ found in sand at Sea- 
field, west of Ireland,” in his possession in 1814, previous to my transmitting to 
the Wermnerian Society an “ Account of the Irish Testacea,’”’ which was publish- 
ed in the Memoirs of the Society, Vol. II. p. 501. I omitted that species, as I 
considered it decidedly foreign, and the true Nerita virginea of Gmelin. It is 
to be met with of all sizes, from two lines to nearly an inch in length. 
Valvaia piscinalis. Mr. Kenyon is unquestionably wrong in considering the 
Valvata pianorbis, ossiorbis, and minuta, as the fry of this species. He should 
keep in view that the young of land and fresh water spiral testacea, have uniform- 
ly a thinness in the outer lip; and consequently the mature shell can at once be 
determined by its thickness, and the solidity of its edge. 
Lymnea fragilis. Mz. Kenyon has entirely mistaken this shell, and has figur- 
ed a variety of the Lymnea palustris for it, and quotes Dr. Fleming. Now the 
Dr. quotes Montagu, and if Mr. Kenyon will refer to that author, Plate XVI. 
Fig. 7. he will find the figure totally different from that which he has given. La- 
marck has completely misplaced this species, by inserting it amongst his Bulimi. 
It would be difficult to conceive how he could have gone into this error, as it was 
Dr. Leach who furnished him with his specimens, and who also gave me that 
shell, from which I made the drawings for the Lymnea fragilis, in my ‘‘ Illus- 
trations of the Conchology of Great Britain and Ireland,” Plate XLII. Fig 22, 
and 23, agreeing in every respect with Colonel Montagu’s original shell, which 
is preserved in the British Museum, and is a species very closely allied to the 
Lymnea stagnalis. 
Lymnea detrita. 1 do not consider this as a British species : it was first in- 
troduced as such by Mr. Bryer, who furnished Colonel Montagu with the speci- 
men from which his figure was taken, Plate XI. Fig. 1. This specimen I care- 
fully examined in the British Museum, and have no hesitation in pronouncing 
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