37G ]\]i. T. II. Wifliers on the 



I. ir>It7-I. 15456, and another more important set com- 

 prising two cariufe (I. 15443-4), one seiitiuu (I. 15445), and 

 a terj^um (I. 15446). 



Measurements. — The following are the measurements of 



the scutum and terguui, and the largest carina : — 



Length. JJreadth. 



mm. mm. 



Carina (PI. V. fig. 15) .... 22-1 (when complete pro- 11-2 



bably about iio mm.). 

 Sciitum(Pl. V. fig. 11) .... lS-2 9-3 



Tergum (PI. V. fig. 12) 17-3 8-4 



Description. — All the valves of this species seen by me 

 from Essen are much worn, and the comparatively coarse 

 sand-grains composing the matrix have in most cases pitted 

 the surface of tlie valves. From certain valves that are 

 Avell preserved it would appear that the surface was origin- 

 ally smooth, except for the faint transverse growth-lines. 



Carina triangular, unusually wide, about twice as high as 

 wide, subcariiiated, transversely semicircular, with the lateral 

 margins slijihtly inflected, basal margin angular, farmed of 

 two curved lines making an angle of about 90°, the outer 

 angles being produced into short spurs ; the apical part of 

 the valve is almost always bowed outwards to a variable 

 extent. The growth-lines follow the outline of the basal 

 margin, but on the inflected lateral edges they are slightly, 

 but rather abruptly, upturned. On the inner surface the 

 lower two-thirds of the valve is deeply concave, and the upper 

 third of the valve is thick and solid', and no doubt freely 

 projected to that extent. Two ridges, much more prominent 

 in some valves than in others, and thickest in the middle, 

 are produced on the solid apical portion, and they project 

 beyond the lateral margins, from which they are separated 

 by a dib^tinct furrow. 



Scutum subtriangular, moderately convex transversely, 

 with the tergo-lateral portion abruptly bent downwards and 

 inwards from the somewhat raised and rounded apico-basal 

 ridge ; occludent margin moderately convex ; basal margin 

 almost straight, about half the width of tlie occludent 

 margin. On the inner surface the inner occludent edge is 

 moderately wide and marked with longitudinal lines ; there 

 is no very deep pit for the adductor muscle, but above the 

 pit the valve is thick and solid ; the a[)ical part of the tcrgo- 

 lateral edge is broken in this specimen, but it appears to 

 liave been much produced inwards, forming a fairly deep 

 furrow betMcen it and the flattened inner occludent edge. 



Tergum subrhomboidal with a straight ajjico-basal ridge. 



