210 KELLIIDiE. 



in 8 fathoms, and I have taken it at Spezzia in 18 

 fathoms. According to Sars it is found in the post- 

 glacial beds of Christiania. 



Clark's account of the animal is that it is " lively, 

 marches with rapidity, and in its course turns from side 

 to side, sometimes resting the shell on the ventral range 

 in an upright posture." Montagu, having found it 

 apparently burrowing in old and thick oyster- shells, be- 

 lieved that it was partly the cause of the small round 

 holes so frequently seen on those shells. Such perfora- 

 tions, however, are attributable to a sponge (Cliona 

 celata), that fills the cylindrical tubes of which the holes 

 are the outlet, and branches off in every direction — a 

 course never known to be taken by any mollusk. The 

 relative proportions of length and breadth in the shell 

 of M. bidentata are very variable. The young are more 

 triangular than the adult, and somewhat resemble in 

 shape the fry of Nucula nucleus. My largest specimen 

 is a line and a half long, and a third more in breadth. 



This small shell has been bandied about by different 

 conchologists from one genus to another, and received 

 various names. Montagu referred it provisionally to 

 My a. Brown in 1827 placed it in the genus Anatina 

 of Lamarck, and Clark did the same in 1855. Gray 

 and Hanley called it a PetricoJa. It is the Erycina 

 faba of Nyst, E. nucleoid of Recluz, and Mesodesma 

 exiguum of Loven. The Montacuta elevata of Stimpson, 

 which Gould supposed was our shell, differs in the posi- 

 tion of the beaks and in other particulars. 



3. M. ferrugino'sa *, Montagu. 



Myafermginosa, Mont. Test. Brit. p. 44, tab. 26. f. 5. Montacuta f err u- 

 ginosa, F. & H. ii. p. 72, pi. xviii. f. 5, 5 a & 5 b (as M. ferruginea). 



Body clear white : mantle having its margins on the ante- 

 * Covered with iron-rust. 



