Pleurotomid:æ. 
Gen. Bela Leach. 
Ved Bestemmelsen af Arterne inden denne Sleet maa 
man uundgaaelig legee til Grundlag Prof. G. O. Sars’s 
Værk ,.Mollusca regions arctice Norvegiæ*; thi der er intet 
tidligere Arbeide, hvori disse nærstaaende Arter saa nøle 
er gransket og hvori er givet saa omhyggelige Tegninger, 
der gjør en Identificeren mulig. 
Prof. Sars har lagt en afgjørende Veet for Artsbe- 
stemmelsen i Piltændernes Struktur og omend jeg maa ind- 
rømme, at enhver Karakter, der er konstant, den være 
taget fra Dyrets indre eller ydre, er berettiget som Arts- 
mærke, saa er det paa den anden Side lidet tilfredsstillende 
for Conchologen kun at have med indre anatomiske Karak- 
terer at gjøre og man kan ikke være tjent med at lade et 
dødt, men velbevaret Exemplar henligge ubestemt, fordi 
Tandbygningen ikke har været undersøgt. Ensidig indre 
Karakterer er ikke praktiske. Tandstrukturens Stabilitet 
maa man ogsaa kunne overse før man kan indrømme en 
Arts Berettigelse, hvor der er Brist paa tilfredsstillende ydre 
Skillemærke. 
Jeg har gjort mig til Qpgave at skaffe saa god Over- 
sigt som muligt over Tændernes Variationer og til den 
Hensigt havt et meget stort Materiale af Slegten Bela 
til min Raadighed. Ikke alene har jeg disponeret over de 
rige Fund fra Expeditionen, Bergens: Museum og min pri- 
vate Samling, men min Ven Conservator Schneider har 
været saa genereux at stille Tromsø Museums meget rig- 
holdige Materiale af Belaarter til min Disposition. 
Inden Familien Buccoude har jeg paavist, at Tæn- 
derne er en lidet paalidelig Karakter og at de er under- 
kastet store Variationer inden Arterne. 
Hos Pleurotomidæ synes det ikke at være saa slemt, 
men Karakteren er langtfra constant og der er al Grund 
at være varsom med Artsdannelser, der har Piltændernes 
Struktur som væsentlig Grundlag. Uden at ville fastslaa det 
som fuldt ud constateret, skal jeg ber dog nævne, at det synes 
som om de geografiske og de bathymetriske Forholde, 
eller med andre Ord de klimatiske Forholde og et paa Grund 
heraf forandret Levesæt har nogen Indflydelse paa Tand- 
strukturen. Ganske paafaldende er det, naar man tager 
Den norske Nordhavsexpedition. Herman Friele: Mollusca. I. 
Pleurotomid:. 
Gen. Bela Leach. 
In distinguishing the species included in this genus, 
we must, of necessity, take as the basis, Prof. G. O. Sar’s 
work — Mollusca regions arcticæ Norwegiæ — because there 
is no earlier work in which these closely related species 
are so precisely investigated, and in which such careful 
illustrations are given to enable their indentification to 
become possible, 
In arriving at a determination of the species, Prof. 
Sars has laid a vital stress upon the structure of the arrow- 
-teeth, and whilst I must admit that every characteristic 
which is constant — whether pertaming to the interior or 
exterior of the animal — is entitled to consideration as a 
specific feature, it is, yet, on the other hand, little satis- 
factory to the malacologist to have to do with the internal 
anatomical characteristics only, and we can not be satisfied 
with permitting a dead, but well-preserved, specimen to 
remain undetermined because the dental structure has not 
been examined. Restricted internal characteristics are not 
practical. We must, also, have a complete survey of the 
stability of the dental structure, before we can admit the 
title of a species where there is a deficiency in satisfac- 
tory external distinguishing features. : 
I have made it my study to obtain the widest pos- 
sible survey over the variations of the teeth and, for this 
purpose, have had a very abundant material of the genus 
Bela at my disposal. Not only have I had the rich col- 
lection from the Expedition, Bergens Museum, and my pri- 
vate collection, but my friend Mr. Schneider, Curator of the 
Tromsø Museum, has been so kind as to place Tromsø 
Museum's very rich collection of Bela species at my disposal. 
In the family of Buccinide, I have shown that the 
teeth are a little reliable characteristic, and that they 
experience great variations in the different species. 
In the Plewotomidæ this does not appear to be so 
graye, but the dental characteristic is far from constant and 
there is every reason to be careful in the formation of species 
having the structure of the arrow-teeth as their material 
basis. Without affirming that it is fully determined, I will, 
here, however, state, that it appears as if the geographical 
and the bathymetrical conditions or, in other words, the 
climatic conditions, and a consequent changed habitus, have 
some influence on the dental structure. It is quite remark- 
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