Bela rugulata, Trosch. for sig at se, at den typiske brede, 
coniske Tandform (Tab. IX, Fig. 1) forekommer langs Kysten 
indtil Tromsø. I Finmarksfjordene afløses den af Formerne, 
afbildet i Fig. 3—4, der danner Overgangen til B. assimilis 
G. O. Sars (Fig. 9, 10). Denne sidste er ikke funden sønden- 
for Lofoten. Og saa kommer den rent arctiske Form spitz- 
bergensis nob. (Fig. 6) med en temmelig afvigende Tand- 
bygning. Alle disse Former hører de mindre Dyb til. 
Dette var den horisontale Udbredning. I de større Dyb 
i vore sydligere Fjorde træffe vi Formen bergensis nob, 
(Tab. IX, Fig. 8) der afviger i sin Tandstruktur fra alle 
Af Arten B, scalaris Møll. har jeg lige- 
ledes i de større Dyb fundet en Form, der har Tænder 
væsentlig forskjellige fra den i de høiere Vandlag (sammenlign. 
Tab. IX. Fig. 17 den typiske scalaris med Fig. 21, 22 
var. abyssicola). 
de foregaaende. 
Deni Tab. LX, Fig. 1—5 afbildede Række Tender til- 
hører alle Bela rugulata forma typica; herfra til var. assimilis 
Fig. 9—10 er kort Vei og ligesaa til bergensis Fig. 7—8. 
Formen spitzbergensis staar eiendommelig isoleret. Tænderne 
kan ogsaa variere hos det enkelte Individ, men, maa jeg 
tilføie, kun en Gang har jeg fundet dette i en paafaldende 
Grad. De 3 Tænder Tab. IX, 9, 9a og 90 tilhører samme 
Individ (8. assimilis) og som en lille Dværg laa Fig. 9a 
imellem de øvrige Tænder; den var dog fuldt udviklet i Form. 
Bela nobilis Møll. og scalaris Møll nærmer sig ogsaa saa stærkt 
til rugulata hvad Tandstrukturen angaar, at de med denne 
Karakter alene neppe fortjener høierer Rang end de foran 
nævnte Former, men her tror jeg ligesom Sars og flere 
andre Forfattere, at der er ganske paalidelige ydre Karak- 
ter, der til enhver Tid vil adskille dem, 
En Gruppe, som baade i ydre Former og Tandstruk- 
tur synes at gaa lige nær over 1 hinanden som den netop 
næynte er B. Trevelyana, decussata, Kobelti, tenwicostata og 
ovals. Tænderne byder her saagodtsom ingen paalidelige 
Skillemærker, og der forekommer ogsaa imellem flere a 
disse Arters Skalformer meget nære Overgange. 
Efter mine Erfaringer vil Belaformerne lade sig rangere 
1 følgende Grupper, som, hvad ydre Form og Piltændernes 
Struktur angaar, viser nærmest Slægtskab. 
Rugulata Gruppen: 
Som felles ydre Karakter kan fremhæves: Vindin- 
gerne kjølede, de axiale Ribber rette (ikke sigmabøiede). Tæn- 
derne varierer tra bred conisk til bred lanseformig. 
Arterne er: Bela rugulata Troseh. 
»  scalaris Møll. 
» nobilis 
Cancellata Gruppen: 
Skallen har de axiale Ribber sigmabøiede; Tænderne 
er sværdformige, = 
Arterne er: Bela cancellata Møll. 
cinered — 
2” 
able that when we examine Bela rugulata, Trosch. we see 
that the typical, broad, conical dental form (Pl. IX, fig. 1) 
occurs along the coast as far North as Tromsø. The 
forms illustrated in figs. 3—4 replace it, however, in the 
Finmark fjords, and form the transition to B. assimilis 
G. O. Sars (figs. 9. 10). The latter is not found south of 
the Lofoden Isles. And now, we have the purely aretic 
form, spitzbergensis nob. (fig. 6) with a considerably diver- 
gent dental structure. All of these forms pertain to the 
shallow depths. ‘This is their horizontal distribution. In the 
great depths of our Southern fjords, we meet with the variety 
bergensis nob. (Pl. LX, fig. 8), which, in its dental structure, 
varies from all the preceding ones. Of the species B. sca- 
laris Møll. I have, also, m the greater depths, found a 
yariety having teeth materially different from that of the 
shallow waters (compare the typical scalaris Pl. IX, fig. 17 
with var. abyssicola figs. 21, 22). 
The series of teeth illustrated in Pl. IX, figs. 1—5 
pertains to Bela rugulata, forma typica; thence, to var. as- 
similis, is only a short step, and likewise, also, to bergensis 
(figs. 7, 8). The variety spitebergensis stands peculiarly 
isolated. The teeth can, also, vary in the individual animal 
but, I must add that, only once have I found this to be the 
case in å remarkable degree. The 3 teeth, (Pl. LX, figs. 9. 
9a and 9 b) pertain to one individual (8. assimilis), and that 
shown in fig. 9a lay, like a little dwarf. between the other 
teeth; its form was, however, fully developed. Bela nobilis 
Møll. and scalaris Moll. approach, also, so closely to 
rugulata in regard to dental structure, that they, from this 
characteristic only, scarcely merit higher rank than the 
previously mentioned forms but, here, I believe, in accor- 
dance with Sars and several other writers, that there 
are quite reliable external characteristics, sufficient, at all 
times, to distinguish them. 
A group which appears, both in external form and 
dental structure, to pass as much over into one another 
as that just mentioned is, B. Trevelyana, decussata, Kobelti, 
tenuicostata and ovalis. Hereg the teeth present almost no 
reliable distinguishing features, and there occur, also, be- 
tween the shells of several of these species very close 
transitions. 
According to my experience, the Bela species may 
be arranged in the following groups, which, both in regard 
to external form and structure of the arrow-teeth, show the 
closest relationship. 
The rugulata group: 
The whorls are angulated; the axial ribs straight, and 
not sigmoid. The teeth vary in form from broad-eonieal, 
to broad-lanceolate. 
The species are: Bela rugulata. Troseh. 
» scalars Møll. 
» nobilis , 
The cancellata group: 
The shell has its axial ribs curved sigmoidally. 
teeth are ensiform. 
The species are: 
The 
Bela cancellata Moll. 
cimered h 
