Polarcirkelen; forekommer i Begyndelsen sammen med B. 
undatum, men i de rent arktiske Have afløser den denne 
fuldstændigt; B. finmarchianum afloser den sydligere B. 
Humphreysianum for atter igjen i Ishavet at blive aflost 
af B. hydrophanwm. 
I min foran nmynte Afhandling “Ueber die Varia- 
tionen der Zahnstructur bei Buccimum” fremsatte jeg den 
Formodning, at flere Arter sandsynhevis bybridiserer og 
begrundede dette i den Omstændighed, at Overgangsformerne 
just er at finde der, hvor flere Arter forekommer talrig 
sammen. B. undatum og groenlandicum findes saaledes i 
stor Mængde littoral ved Hammerfest, og her løbe ogsaa 
begge Former fuldstændig i hinanden; ved Spitsbergen, hvor 
flere Arter, saasom B. groenlandicum, undulatum, glaciale og 
Terræ Nowe forekommer sammen, vil man ligeledes finde 
Former, overfor hvilke man vil staa meget tvivlsom, og som 
gjør bestemt Indtryk af blandet Herkomst. 
Et lignende Forhold, som her er nævnt, finder ogsaa 
Sted paa den amerikanske Side. Der mødes de nordlige 
og arktiske Former under en langt sydligere Breddegrad, 
og at dømme efter hyad jeg har seet, er Forvirringen mel- 
lem Arterne der end større. Herr Verkriizen har bragt 
smukke Svitter af Buceina med sig fra Nyfundland og der- 
imellem bar han fundet ikke mindre end 5 nye Arter, 
hvorat dog en eller to maaske endnu ikke er beskrevet. 
De 3 af disse har jeg havt Anledning at se, men omend 
de neppe vil blive erkjendt for gode Arter, saa er de dog 
interessante Mellemformer. De store og flittige Skrabninger, 
som U. S. Fish Commission foretager, vil rimeligvis bringe 
et stort Materiale sammen, og utvivlsomt kan man vente 
sig værdifulde Bidrag til denne Slægt derfra, naar det en 
Gang bliver offentliggjort. 
At Tandstrukturen ingen Betydning har som Arts- 
karakter inden Buccimwm er før næyrnt. Der kun to 
Tandformer, nemlig B.undatums og B. groenlandicums, den 
første med en Centralplade, med 5 til 7 Tænder og Side- 
pladerne med + Tænder; den sidste med en 3- til 5-tandet 
Centralplade og 8-tandet Sideplade, men forøvrigt gaa begge 
Tandformer hyppig over i hinanden og er 1 det Hele taget 
underkastet stor Foranderlighed. 
er 
Paa. Pl. V, Fie. 16 & 17, er fremstillet 2 Variationer 
af B. undatums Tender, og dette maa være nok for at vise, 
hvor liden Støtte der ligger i denne Karakter. Fig. 16 er 
i den Grad atvigende fra hele Familiens Tandtype, at den 
gaar ind paa Fusciolaridernes Grændser; Fig, 17 viser, at 
Tændernes Antal paa Centralpladen hos det selysamme In- 
divid kan voxe fra 6 i den forreste til 8 i den bageste 
Del af Radula. B. groenlandicum frembyder lige store 
Variationer i sin Tandbygning. 
limits. Thus, for instance, B. groenlandicum is first met 
with north of the Polar Circle in the European waters of 
the Atlantic, and here it occurs at first im company 
with B. undatum; but in the true. Arctic Seas it wholly 
supplants that species. And again, B. finmarchianwm takes 
the place of the more southerly form, B. Humphreysianum, 
to be in turn succeeded by B. hydrophanum. 
In the above-mentioned paper, “Ueber die Variationen 
der Zahnstructur bei Buccinwm,” I ventured to assume that 
some of the species are hybrids, and founded my assump- 
tion on the fact. that transition-forms are found in lo- 
calities where several species frequently occur together. To 
give an example: — B. undatum and B. groenlandicum are 
both numerous in the lttoral zone at Hammerfest, and here 
the two forms pass completely over into each other. At 
Spitzbergen, too, a locality in which several species, such 
as B. groenlandicum, undulatum, glaciale, and Terre Nove 
occur together, forms will be met with that convey the im- 
pression of specific mixture. 
The same is the case on the American side. There, 
the northern and Arctic forms meet much farther south, 
and, to judge from what I have seen, the confusion of spe- 
cies must be still greater. Mr, Verkriizen brought home 
from Newfoundland a rich collection of Buccina, compri- 
sing among them as many as 5 new species, one or two of 
which are possibly still undescribed. Three of these new 
species I have had opportunity of examining, and though 
their rank as true species may be doubted, they must 
still -be regarded as interesting transition-forms. The 
frequent and extensive dredging operations carried on by 
the U, 8. Fish Commission, will in all probability bring to 
light a rich material. and valuable information concerning 
this genus may unquestionably be expected from that 
quarter. 
That no importance can be attached to the dentition 
as å specific character in the genus Buccinum, has been 
already stated. There are only two forms of teeth, viz. 
that in B. wndatwm and in B. groenlamdicum the former has the 
central plate with from 5 to 7 cusps and the laterals with 
4 each; the latter has from 3 to 5 cusps on the central 
plate and 3 on the laterals; for the rest, however, both 
forms frequently merge into each other, and on the whole 
the character is exceedingly liable to vary. 
In Pl. V, figs. 16, 17, are represented two cases of 
structural diversity occurring in the teeth of B. undatum, 
amply sufficient to show the untrustworthiness of this char- 
acter. In fig. 16, the structure differs to that extent 
from the typical dentitior of the family. as to have features 
in common with those of the Fasciolaridæ. Fig. 17 shows 
that, in one and the same individual the number of cusps 
on the central plate can increase from 6 at the anterior, to 
8 at the posterior, end of the radula. B. groenlandicum 
exhibits as great a structural variation. 
4* 
