24 



as in the other species, spoon-shaped. But there^is a very strongly developed external ligament 

 of horn-brown color, projecting from the umbones, and extending half way between them and 

 the posterior extremity. 



The cardinal teeth are numerous, but somewhat various in number. They are however 

 always most numerous in the posterior part, where their number may even amount to 27. 

 In the anterior part there are usually about 14 teeth. In 6 specimens, the following pro- 

 portions were observed. 



Dentes anteriores 14 posteriores 24 

 14 22 



11 18 



13 19 



14 27 



15 27 



Of the muscular impressions (see fig. 18) the posterior is largest, and of an oval- 

 triangular form, and, like the anterior, situated high up under the border of the hinge. The 

 ptillinl impression has towards its posterior part a deep rounded sinus, which extends nearly 

 to the middle of the length of the shell. 



Very small specimens (fig. 20) of 5 millimetres in length, have the ventral border 

 somewhat less curved, and the posterior border more straightly truncated. In such small 

 specimens, the shell is quite transparent, so that the animal may be distinctly seen through 

 the shell. 



The. animal is highly remarkable by the proportions of the siphons, of which the anal 

 (a) is quite unusually long, namely more than the whole length of the shell, and usually more 

 or less curved or crooked downward at the extremity; while the branchial (b) is particularly 

 short, and scarcely projecting beyond the posterior border of the shell. 



Between the two there is observed a long filiform appendage (c) nearly of the same 

 length as the anal siphon, doubtless a pallial tentacle. 



The foot (d) is of the usual shape in this Genus, forming at the extremity a widened 

 creeping-disc, wliich consists as it were of 2 lobes and is crenulated at the edges. Above 

 this in the middle of the body, the crescent-formed transversally placed gills (e) may be 

 seen, and above these again a semi-circular dark line (f), curved towards the umbones, which 

 is the intestinal canal filled with excrement. 



The present species seems to be widely diffused in the great depths off our coast. 

 It was, as has been already stated, first discovered in the Herl0fjord near Bergen by M r . Con- 

 servator Koren. L have myself found it pretty often in the great deeps at Lofoten, in 200 

 400 fathoms ; also in the Hardangerfjord, where it goes down to 500 fathoms, and lastly during 

 my recent stay at Aalesund, in the so-called Brei-sunds deep in 200 fathoms. It occurs every 

 where, like the other species of this Genus, only on a bottom of soft clay or mud. 



The species may be known by the following diagnosis. 



