ee 
1865.] MR. O. A. L. MORCH ON THE VERMETID. = 
different lingual dentition. The same is the case with Tritonium 
undatum (L.) and the Arctie Tritonium grenlandicum (Ch.), which 
are chiefly distinguished by the different consistence of the testaceous 
matter, but vary in the size, shape, and sculpture of the shell in an 
analogous manner, as the following scheme will show :— 
1. Tritonium undatum, L. 1. Tritonium undulatum, Moll.= Bucci- 
num labradorense, Reeve. 
2. Buccinum acuminatum, Brod. 2. A similar form is known from Green- 
land by five specimens. 
3. ciliatum, auct. Brit. 3. Tritonium grenlandicum, Ch. 
4. humphreysianum, Bennet. 4. —— humphreysianum, Moll. 
The variation of the quasi-parasitical species, however, almost 
surpasses belief. One of the most striking instances is the Patella 
compressa (L.), which owes its remarkably compressed form to its 
habit of affixing itself to the stems of the large seaweeds of the Cape 
of Good Hope. When it drops from its place, and is received on a 
flat object, an expanded limb is added to the edge, of a somewhat 
coarser sculpture, and the uniform yellowish colour is changed to 
a whitish colour mottled with red spots, which proves clearly ‘» at 
this species is undoubtedly a form of Patella miniata, Born. vr. 
Gray even mentions a specimen which is first a Patella miniata, 
then a P. compressa, and ultimately again a P. miniata. When 
the latter form becomes full-grown*, ‘caput iufantis superans’’ +, 
it is the Patella rustica of Linneus. These three forms are by 
several authors placed in three different genera. These facts prove 
clearly the necessity of comparing extensive series of specimens be- 
fore new species are established. It was very difficult for me, when 
I wrote my papers on the Vermetide, to procure numerous speci- 
mens of all the species, as this family has been very much neglected 
by collectors. I have, however, been able to compare sufficiently 
large suites of one or two species of each genus. I have most com- 
pletely described all the different varieties of age and growth of 
Vermetus conicus, Dill. (P. Z. 8. 1861, p. 341). I have convinced 
myself, by numerous dissected specimens, that this species is first a 
Petaloconchus with internal laminz, then a Bivonia (Carp.) with 
lire on the columella, without lamine, and finally an Aletes (Carp.) 
with suddenly dilated whorls and a nearly smooth columella. I 
have only found the young in the latter form of shells. Finding it 
useful, or even necessary, to have a nomenclature for these differ- 
ences, I have used these now superfluous generic terms for that pur- 
pose, in the same manner as the term Cysticercus is generally used 
for a stage of Tenia, or Zoéta for the young Crab. 
I some time ago got a specimen of Fasciolaria princeps from Ma- 
zatlan, with several solitary specimens of Bivonia contorta (Carp.) 
attached, two of which, after making three or four whorls, suddenly 
enlarge the aperture of the tube to twice its diameter, and change the 
dark-brown strongly granulated surface to a pale-yellowish nearly 
* Gray, Guide to the Systematic Distribution of Mollusca, p.175; and Sowerby, 
Genera, fig. 3, Patella. 
+t Museum Ludovice Ulrice, p. 694. 
Proc. Zoou. Soc.—1865, No. VII. 
