34 



close against the middle lobe (see fig. 10); when the foot is fully extended the side lobes are 

 turned energetically outwards and backwards, at the same time that the whole foot twists 

 itself to one side or to th* other, alter which it is again withdrawn into the shell with a 

 rapid jerk. This is repeated at gi-eater or smaller intervals; and each time the shell is moved 

 a little forwards in one direction or in another. The protraction and the retraction take place 

 so suddenly and unespectedly, that I had at first the greatest trouble in getting a correct idea 

 of the form of the foot; and it was only by many repeated observations that I succeeded 

 completely at last. This is very difterent from what we observe in our other 2 Dentalia, in 

 which the movements of the foot are far slower, and the whole animal is much less sensitive. 

 When tirst the foot of these species is extended, we can quietly and leisurely observe it from 

 all sides ; nay I have often taken such a Dentalium up out of the water without the foot 

 being reti'acted. 



I have found this peculiar deep-sea form not very rarely at the fishing-place Skraaven 

 in Lofoten, but always only at the greatest depths, 200—300 fathoms, while the D. abyssorum 

 is found up to 40 fathoms depth. Lately I have met with the same form again far more 

 to the south, namely in the neighborhood of Aalesund, and also here only at the greatest 

 depths which occur, namely in the so-called Breisunds-deep in 200—220 fathoms in muddy 

 bottom. Our species may be characterised in the following manner: 



Dentalium agile. M. Sars. 



Testa teres, valde angusta, parum arcuata interdum fere recta; posteriora versus in 

 tota longitudine a;qualiter attenuata, albida sub-opaca parum nitida; posteriore parte sspius 

 obscurior, apice tenuissimo oblique truncato rimato et tubulo ornato supplementario parum 

 prominente. Superficies testae plerumque la!vis striis modo iucrumenti circularibus obducta, 

 rarior in posteriore parte longitudinaliter striata, striis vero parum distinctis et vix costellaruni 

 instar prominentibus. 



Animal quam solito agilius. Pes cylindricus apice ut vulgo trilobate, lobo mediano 

 conico-acuminato, lateralihus membranaceis et plicatis; et protractio et retractio ejusdem 

 celerrima. Appendix scapha^formis corporis postice sat elongata iuajquilateralis incisura ventrali 

 longa et angusta fissa. Longit. test* raajorum 58 Mm. diametr. apertur* 4 Mm. apicis 1 Mm. 



Habitat nou infrequens ad insulas Lofotenses in profunditate 200—300 orgyarum fundo 

 argillaceo nee non prope urbem Aalesund prof. 200 org. Ceterum fossilis in tellure tertiaria 

 Calabriffi inventa (D. incertum Philippi (nou Deshayes). 



Philippi's short description of his Dentalium incertum, which however according to 

 Jeffreys is different from the form described by Deshayes under the same name, suits our 

 northern Form precisely; and Jeffreys has also, according to his obliging communication, by 

 comparing specimens of our form with the fossile form from Calabria, ascertained that the 

 two agree perfectly. We have thus here again an interesting instance of the animals of 

 earlier telluric periods having been able to continue their existence undisturbed in the great 

 deeps of the Ocean up to cm- own time. 



