188 SILURIAN MOLLIT^CA. 



tary ridge, which is about a line below the hinge-margin. This 

 differs from the D. obtusa (M*^Coy) in its narrow, elongate ellip- 

 tical figure and less gibbosity. 



Tilestone of Storm Hill, Llandeilo. 



[Col. University of Cambridge.) 



Dolahra obtusa (M'Coy). 



Sp. Char. 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 sub truncate, the inferior angle 

 obtusely rounded; posterior slope abrupt, inclined, the dia- 

 gonal ridge obtusely rounded ; surface nearly smooth. Width 

 10 lines, length 1 inch 5 lines, greatest depth of one valve 

 (half-way between the beak and posterior angle) 4 lines. 



This species is more obtusely rhomboidal, and is more obtusely 

 keeled, has a longer hinge, and is much less elongate than the 

 Cucullcea amygdalina (Phill.), which is only a common variety of 

 the C. unilateralis (Sow.), from which this differs by its thick 

 posterior tooth, &c. The 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 shows obscure traces of serrature, which may be owing 

 to the roughness of the matrix. 



Tilestone of Storm Hill, Llandeilo. 



[CoL University of Cambridge.) 



Anodontopsis (M^Coy), n. g. 

 = Microdon ? Conrad (not Agassiz nor Meigen). 

 Gen. Char. Equivalve, inequilateral, compressed; general form 

 rotundato-quadrate or subtrigonal ; posterior side wide, round 

 or obliquely subtruncate, anterior end shghtly contracted in 

 front of the beak ; beaks small, prominent, nearer to the an- 

 terior 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 

 muscular impression simple, ovate, longer and stronger than 

 the posterior ; occasionally a slight clavicular extends from in 

 front of the beak behind the anterior adductor impression 

 leaving a furrow in the cast ; pallial impression entire (occa- 

 sionally one small cardinal tooth beneath the beak) ; surface 

 smooth or concentrically lined. 



Except in their small size and marine habits, these little fossils 



