27 



Polarcirkelen ; forekommer i Begyndelsen sammen med />'. 

 undatum, men i de rent arktiske Have afløser den denne 

 fuldstændigt; li. finmarchianum afløser den sydligere B. 

 Humphreysianum for atter igjen i [shavel at hine afløst 

 at li. hydrophanum. 



I min foran nævnte Afhandling "Ueber die Varia- 

 tionen der Zahnstructur bei Buccinum" fremsatte jeg den 

 Formodning, at tirre Arter sandsynligvis hybridiserer og 

 begrundede dette i den Omstændighed, at Overgangsformerne 

 just er at tinde der. hvor Uere Arter forekommer talrig 

 sammen. />'. undatum og groenlandicum tindes saaledes i 

 stur Mengde littoral ved Hammerfest, og her lobe ogsaa 

 begge Former fuldstændig i hinanden; ved Spitsbergen, hvor 

 tiere Aiier. saasom li. groenla ndicum . undulatum, glaciate og 

 Tim/ Novce forekommer sammen, vil man ligeledes tinde 

 Former, overfor hvilke man vil staa mettet tvivlsom, og som 

 gjør bestemt Indtryk af blandet Herkomst. 



Et lignende Forhold, som her er nævnt, tinder ogsaa 

 Sted paa den amerikanske Side. Der modes de nordlige 

 og arktiske Former under en langt sydligere Breddegrad, 

 og at dømme etter hvad jeg har seet, er Forvirringen mel- 

 lem Arterne der end større. Herr Verkriizen har bragt 

 smukke Svitter af Buccina med sig fra.Nyfundland og der- 

 imellem har han fundet ikke mindre end 5 nye Arter. 

 hvoraf 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 Mellomformer. De store og flittige Skrabnihger, 

 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 Buccinum er før nævnt. Der er kun to 

 Tandformer, nemlig B.undatums og B. groerilandicums, den 

 teiste med en Centralplade, med 5 til 7 Tænder og Side- 

 pladerne dum! -i. Tænder: den sidste med en 3- til 5-tandet 

 Centralplade og 3-tandet Sideplade, men forøvrigt gaa begge 

 Tandformer hyppig over i hinanden og er i det Hele tåget 

 underkastet stor Foranderligbed. 



Paa pi. v. Fig. 16 & it, er fremstillet 2 Variationer 

 af B. undatums Tænder, og dette maa være nok tor at vise, 

 hvor liden Støtte der ligger i denne Karakter. Fi^r. Hi er 

 i den Grad afvigende fra hele Familiens Tandtype, at den 

 gaar ind paa Jfhsciolaridernes Grændser; Fig. it viser, at 

 Tændernes Anta] paa Centralpladen hos det selvsamme In- 

 divid kan voxe fra lj i den forreste til 8 i den hageste 

 Del af Hadula. B. groenlandicum frembyder lige store 

 Variationer i sin Tandbvgnine. 



limits. Tims. tor instance, 11. groenlandicum is first met 

 with north of tlie Polar Circle in the European waters of 

 tlie Atlantic, and here it occurs at first in company 

 with />. undatum . but in the true Arctic Seas it wholly 

 supplants that species. And again, />'. finmarchianum takes 

 the place of the more southerly form. li. Humphrey sia/num, 

 to be in turn succeeded h\ /;. hydrcphanum. 



In the above-mentioned paper, "Ueber die Variationen 

 der Zahnstructur bei Buccinum" 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 littoral zone at Hammerfest, and here 

 the 1 two forms pass completely over into each other. At 

 Spitsbergen, too. a locality in which several species, such 

 as /;. groenlandicum, undulatum, glaciale, and Terra Novæ 

 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. S. 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 a specific character in the genus Buccinum, has been 

 already stated. There are only two forms of teeth, viz. 

 that in II. undatum and in B. groenlandicum : 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 Pi. 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 ti^-. Hi. the structure differs to that extent 

 from the typical dentition of the family, as to have features 

 in common with those of the Fasciolaridoe. Fig. n 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. 



