SILURIAN MOLLUSCA. 193 



behind tlie vertical line of the beaks ; surface rugged, with 

 strong, thick, irregular wrinkles from the anterior end, be- 

 coming obsolete on the posterior slope. Width from beak to 

 ventral margin 1 inch, length 1 inch 5 lines, depth of one 

 valve about one-third of the width. 



This is somewhat allied to the Cypricardia retusa (Sow.), but 

 has the anterior end even more vertically truncate ; it is more 

 elongate (although in this point it varies considerably) ; but it is 

 most obviously distinguished by the strong wrinkling of the sur- 

 face, parallel with the ventral edges, by which latter, as well as 

 the great depth of the truncated anterior end, it also differs from 

 the C. impressa (Sow.). 



Upper Ludlow rock, Benson Knot, Westmoreland. 



(Col. University of Cambridge.) 



Modiolopsis inflata (M'Coy). 



Sp. Char. Longitudinally oblong, very gibbous ; beaks obtuse, 

 incurved, large, close to the anterior end, which is large and 

 obtusely rounded ; an obtuse sigmoidal ridge extends from the 

 beak to the posterior inferior end, which is elliptically rounded 

 to the very obtuse cardinal angle, which is slightly elevated ; 

 hinge-line little more than half the length of the shell, with a 

 slender cartilage ridge just below it ; ventral margin very 

 slightly concave in front of the diagonal gibbosity. Width 

 9^ lines, length 1 inch 6 lines, greatest depth of one valve 

 (about one-third the length from the beak) 4 lines. Surface 

 with minute irregular plications and lines of growth. 



Pen Cerrig Serth (very common). 



Distinguished from all the varieties of the M. modiolaris by its 

 greater gibbosity, shorter hinge-line, and broader anterior end. 

 {Col. University of Cambridge.) 



Modiolopsis (? Orthonota) postlineata (M'Coy). 



Sp. Char. Oblong, twice as long as wide, shell thin, moderately 

 convex ; beaks small, near the anterior end, which is obtusely 

 rounded; no byssal sinus; posterior end obtuse, obhquely 

 rounded ; dorsal and ventral margins nearly parallel, straight ; 

 hinge-line two-thirds the length of the shell, with a nearly 

 parallel delicate hinge-plate running beneath it and nearly 

 parallel with the erect dorsal margins ; surface with minute 

 obsolete transverse wrinkles of growth, except of the flattened 

 posterior slope, which is radiated with fine close equal striae 

 from the beak. Width from the beak to the ventral margin 

 5 lines, length 1 inch. 



Some specimens bear a rough general resemblance to the Nu- 



N 



