8 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NOV. 5, 



18. Pecten crebristria, De Kon. PL IV. fig. 5. 



The shape of this small Pecten is almost completely circular ; its 

 valves are slightly, but regularly convex. The surface is covered with 

 a large number of small, radiating ribs, often bifurcated, of unequal 

 thickness, and irregularly distributed upon the whole surface of the 

 valves. The lines of growth are feebly expressed, and are only well 

 seen with the lens. The ears are small and rectangular. 



The length of the only known specimen is 16 millimetres, its 

 breadth is 14 millimetres. 



19. Solenopsis imbricata, De Kon. PI. IV. fig. 3. 



This species is transverse, and almost three times as long as wide. 

 Its anterior side is very short, and its margin rather regularly semi- 

 circular; the posterior side is bounded by a curve, approximating to 

 an ellipse. The ventral edge is feebly sinuated. The beaks are very 

 small, and hardly project above the dorsal border. The surface is 

 smooth ; one may observe six or seven imbricated lamella? parallel to 

 the ventral edge ; they have been formed by the successive growth 

 of the shell. The valves are depressed and very shallow. 



The length of the largest of the two known specimens is 17 milli- 

 metres, and the width 44 millimetres. Prom the Productus-lime- 

 stone of Vurcha. 



20. Dentalitjm Hercttletjm, De Kon. PL IV. figs. 10-12. 



This species is remarkable on account of its great size and the 

 considerable thickness of its shell. It has the greatest analogy with 

 my D. ingens of the Carboniferous Limestone of Vise. Like that spe- 

 cies, its surface is covered with irregular stria? of growth, and is 

 rendered rugose by their presence ; these stria? are a little oblique to 

 the axis, and show that one edge of the aperture of the shell must 

 have been slightly produced. They differ by the regular, conical 

 shape, and by the greater thickness of the shell of D. Herculeum, as 

 shown by the transverse sections represented in PL IV. figs. 10 a 

 & 12 a, and the longitudinal section, fig. 11. The section, fig. 12 a, 

 offers again another peculiarity, consisting in the presence of a very 

 prominent longitudinal fold, which transforms the interior of the 

 shell from a circular into a semicircular form. This shape is merely 

 accidental, and is exhibited only by a single specimen among the 

 seven submitted to my examination. 



The largest of these specimens was 7 centimetres long, and 1| in 

 diameter on the side of the aperture ; but it is probable that com- 

 plete specimens attained at least 15 centimetres in length. 



21. Bellerophon dectpiens, De Kon. PL III. fig. 1. 



This is one of the most remarkable of all the species with which I 

 am at present acquainted ; it is a little longer than wide, and its 

 surface is almost smooth. The dorsal band produced by the buccal 

 sinus is very narrow, and very slightly apparent. The ribs of growth 

 are very wide, and it would have been difficult to distinguish them 



