MONTACUTA. 209 



protruded considerably beyond the shell and fringed with bril- 

 liant silvery, close-set, symmetrical, blunt, short but distinct 

 indented points, which extend on both sides to near the beaks : 

 tube scarcely perceptible, lying within the posterior margin of 

 the shell : foot very large, long, broad, subtriangular, hyaline, 

 sprinkled with flake-white spots ; it is slightly bent or genicu- 

 late, and has a conspicuous byssal groove. 



Shell triangularly oval, or of a somewhat rhomboidal 

 figure, compressed, rather solid and opaque, of a more or less 

 dull aspect : sculpture, irregular lines of growth, and (occa- 

 sionally) white longitudinal lines or streaks as in the last 

 species : colour milk-white : epidermis not very thin, pris- 

 matic, and marked with numerous minute concentric striae 

 which impart to it a silky appearance under the microscope : 

 margins abruptly truncate at the smaller or posterior end, 

 nearly straight or slightly curved in front, expanding and 

 rounded at the anterior end, and very gently sloping behind 

 from the beak to that side : beaks small and blunt, promi- 

 nent, somewhat incurved, with an indentation below ; they 

 are placed very much nearer the posterior side, which is not 

 one-third the size of the other : hinge-line nearly rectan- 

 gular, occupying about one-third of the circumference : car- 

 tilage yellowish, smooth, thick and globular, contained in a 

 triangular pit lying directly under the beak in the left valve, 

 and forming a cup-shaped process or ossicle at its base : hinge- 

 plate narrow but strong, deeply excavated in the middle for 

 the reception of the cartilage, which sometimes encroaches on 

 the beak to such an extent as to make the latter appear broken 

 or eroded : teeth, in the right valve rather short, leaf- like, and 

 diverging inwards ; in the left valve longer, and parallel with 

 the hinge-line ; those on the anterior side are the largest in 

 both valves : inside nacreous and glossy, with a plain margin : 

 scars obscure. L. 0-125, B. 0*14. 



Habitat : Muddy gravel and in the crevices of old 

 bivalve shells, from 10 to 70 fathoms, everywhere from 

 Unst to Guernsey. As an upper tertiary fossil it is 

 recorded by Grainger from Belfast, by James Smith from 

 Bridlington, and by Searles Wood from the Red and 

 Coralline Crag. Its foreign range extends from Norway 

 to Sicily. Malm has dredged it on the Swedish coast in 

 10-25 fathoms, M f Andrew at Vigo in % and. off Sicily 



