69 
V. Further Observations on the Metamorphosis of Gasteropoda, and the Affinities of cer 
• tain Genera, with an attempted Natural Distribution of the principal Families of th 
Order. By John Denis Macdonald, Assistant Surgeon of H. 31. S. " Herald, 
Capt 
H. M. Denham, B.N., F.B.S. Communicated 
Professor Hr 
F.R.S., F.L.S. 
Read February 16, 1860. 
IN offering to British Zoologists the following remarks on the metamorphosis of Gaste 
•pod 
I 
am anxious to premise that, as my present opportunities of consulting the 
researches of others in this field are extremely scanty, it is quite possible that my inde- 
pendent observations may appear to be but newly garbled statements of already published 
facts 
prop of simpl 
I am willing, however, to risk this, feeling that confirmation, which is the only 
tion however truthful, must widen the basis of even accepted 
If such confirmation be afforded by this paper, it will not be altogether unimportant ; 
but if the facts are new, which they are likely to be, so much the better. 
When I first recognized a conformity in the dentition of numerous pelagic Gasteropods 
with that of certain clearly defined families, the inference was natural enough, that thos< 
little creatures formed a gronp in themselves, admitting of a like classification, thougl 
still, as it were, of a representative value zoologically speakin 
i 
Another idea, however 
gained weight in my mind, namely, that they were merely the larval forms of genera bet- 
ter known to us in their perfect or adult state. This view I have endeavoured to sustain, 
in a former paper, with the evidence available at the time ; and however inconclusive 
the arguments then adduced may have been, I am qnite satisfied that the facts and 
materials since obtained will place it beyond all reasonable doubt 
While H. M. S. " 
Herald" lay at anchor on the leeward side of the Wreck* and Catot 
Reefs, the tideway cansed by the water sweeping 
over and around those obstructions 
brought many interesting objects to the towing net, including several genera of pelagic 
Gasteropoda, with which we are more immediately concerned in the present paper. 
To enter at once into particulars, I first observed a little shell bearmg the toothed a „d 
sinuated lip of a Ckeletropis, and appearing to be a new specxes of that genus ;Hkm9 
been previously placed on my guard against this deceptive resemblance, whnm I detected 
in another instance, I watched the movements of the occupant the more closely I soon 
found that the great activity of the little creature and the peculiar form of * foot, u Inch 
had a broad anterior margin, sloping sides, and a bifid postenor estrenuty gave ^endence 
e tit „™ . « f i wliPTi its linamal dentition was examined 
of its being the young of a speexes of Nassa and .hen £ ^ ^ 
under the microscope, this proved to be the case. 1 may lemar* « mnlw L„ 
iW is distinguished from that of Succinum and ***** by he absence £ sma^ , den- 
tides between The two principal fangs of the pleura,, so character*!* of the *»*. 
* Lat. 22° 10' 30". Long. 155° 30' 00". 
f Lat. 23° 15' 00". Long. 155° 35' 00" 
