270 BRITISH PALAZOZOIC FOSSILS. [ LAMELLIBRANCHIATA. 
This differs from the D. obtusa (M°Coy) in its narrow, elongate, elliptical figure, and less gibbosity. 
Position and Locality—Tilestone of Storm Hill, Llandeilo, Caermarthenshire. 
Explanation of Figures —P). 1. L. fig. 10. Natural size of right valve; fig. 10 a, Ditto profile. 
Dotapra optusa (M’Coy). Pl. 1. K. fig. 30. 
Ref—Id. M°Coy, Ann. Nat. Hist. 2nd Series, Vol. VII. p. 53. 
Sp. Ch.—Obliquely ovate, width about three-fifths of the length, gibbous ; beaks large, obtuse, nearly in the 
centre of the hinge-line, and one-fourth of the length from the anterior end; anterior end small, gradually 
curving into the ventral margin, which is only slightly convex, oblique to the hinge-line ; posterior end obliquely 
subtruncate, the inferior angle obtusely rounded ; posterior slope abrupt, inclined, the diagonal ridge obtusely 
rounded ; surface nearly smooth. Width ten lines, length one inch five lines, greatest depth of one valve (half- 
way between the beak and posterior angle) four lines. 
This species is more obtusely rhomboidal, and is more obtusely keeled, has a longer hinge, and is much 
less elongated than the Cucullwa amygdalina (Phill.), which is however only a common variety of the C. wnt- 
lateralis (Sow.), from which this differs by its thick posterior tooth, &c. The very thick, elongate, posterior 
tooth in the right valve is simple, and about two-thirds the length of that part of the hinge-line from which it 
declines ; in some parts the hinge-line shews obscure traces of serrature, which may be owing to the roughness 
of the matrix. 
Position and Locality—Tilestone of Storm Hill, Llandeilo, Caermarthenshire. 
Explanation of Figure-—P1. 1. K. fig. 30. Natural size, of right valve. 
Genus. ANODONTOPSIS (A/°Coy). 
Syn. ~ Microdon? Conrad (not Agassiz nor Meigen.) 
Gen. Char.—Equivalve, inequilateral, compressed ; general form rotundato-quadrate or subtrigonal; pos- 
terior side wide, round, or obliquely subtruncate, anterior end slightly contracted in front of the beak; beaks 
small, prominent, nearer to the anterior than the posterior end; hinge-line shorter than the shell, with a 
posterior, long, slender, lateral tooth, or cartilage-plate, extending just below it, (double in the right valve), and 
another similar but shorter one in front of the beaks: anterior and posterior muscular impressions simple, 
ovate, the latter longer and stronger than the anterior; occasionally a slight clavicular ridge extends from in 
front of the beak behind the anterior adductor impression, leaving a furrow in the cast; pallial impression 
entire ; (occasionally one small cardinal tooth beneath the beak ;) surface smooth or concentrically lined. 
Except in their small size and marine habits these little fossils resemble the recent Anodons, from which 
there being but two simple adductor impressions separates them. They differ from Modiolopsis (or Cypricar- 
dites) in their rotundato-quadrate compressed form, and the posterior adductor impression like the anterior one, 
and they have no trace of the byssiferous sinus so common in that group between the body of the shell and the 
anterior side; from Schizodus (Myaphoria), with which Prof. King seems to have blended them, they are distin- 
guished by the long, slender, posterior cartilage plate or lateral tooth, a little below the hinge-line. Except in 
form they are identical with Clidophorus, and should be considered but as a subgenus thereof, distinguished from 
those long narrow types by their broad rounded or oblique axe-like form, more prominent beaks, and less marked 
clayicular ridge. From the figure of Microdon bellastria (Conrad), I should have imagined it belonged to the 
present genus, but his description of the hinge renders it probable that this genus is different ; and I accordingly 
give a description of my own clear types; besides which the name Microdon was applied long previously to a 
genus of Fish, and one of Insects, 
