New Species of Panenka. 403 



inches, strongly compressed at the sides, though perhaps 

 abnormally so, subovate in marginal outline, about one- 

 third longer than high and highest posteriorly, the greatest 

 height, exclusive of the beaks, being at or near the pos- 

 terior termination of the cardinal border. 



Anterior side produced and somewhat pointed, its outer 

 margin sloping obliquely and rapidly downward from the 

 cardinal border above, and forming a rather narrowly 

 rounded junction with the ventral margin below: posterior 

 side about equal to the anterior in length, but broader in 

 the direction of its height and much more broadly rounded 

 at the end : ventral margin moderately convex and most 

 prominent posteriorly, nearly straight but ascending very 

 gradually in the centre and anteriorly : superior border 

 rearly straight or but slightly convex on each side of the 

 beaks, curving gradually and somewhat convexly down- 

 ward at each end, but rather more rapidly so at the pos- 

 terior end than at the anterior : umbones oblique, prominent, 

 central : beaks curved inward and a little forward. 



Surface marked by from thirty-five to forty large, simple 

 and rounded radiating ribs, which are nearly straight an- 

 teriorly, but slightly curved in the centre and posteriorly, 

 also by numerous and unequal concentric lines of growth. 

 In some specimens an occasional intermediate and very 

 much smaller rib is developed between two of the larger 

 ones. Characters of the interior of the valves unknown. 



The figure on plate 1 is of the natural size. The speci- 

 men which it represents is the most perfect of the right 

 valves collected, and measures 16.2 cm., or six inches and 

 four-tenths, in length, and 10.7 cm., or four inches and two- 

 tenths, in maximum height, inclusive of the beak. It does 

 not happen to show any of the smaller intermediate ribs 

 nor the concentric lines of growth mentioned in the descrip- 

 tion of the species, these being seen in other specimens. 

 The shell attains to a much larger size than the specimen 

 figured, for an imperfect right valve collected by Mr. 

 Lambo was probably a little more than nine inches in 



