27 



surface partially covered with small undulations, arranged in an obscurely 

 concentric manner, as shown in fig. 3, pi. 2. Neither the area nor the 

 internal characters are seen in any of our specimens. 



Locality and Formation. — Between Cape Rosier and Cape Gaspe ; in 

 limestone No. 1, Lower Helderberg ; occurs also in the Lower Ilel- 

 derberg series in New York. 



Collectors.— ^iv W. E. Logan, R. Bell. 



Strophomena ruomboidalis. (Wilckins.) 

 This species has been found in Nos. 1, 5 and 8 of the Gasp6 series. 



Strophomena Irene. (N. sp.) 



Plate 2, figs. 5, 5a. 



Descri'ption. — Shell large, nearly flat ; cardinal angles usually slightly 

 projecting ; sides in the posterior half either straight and sub-parallel or 

 gently concave and converging towards the front ; anterior half broadly 

 rounded ; front margin sometimes nearly straight in the middle. Width 

 on the hinge line usually from two to three inches ; length from one-sixth 

 to one-third less than the width. 



The ventral valve is very slightly and uniformly convex, most elevated 

 about the middle or a httle above, compressed towards the cardinal 

 angles ; umbo and beak small ; area about two lines high at the beak in a 

 specimen 2 J inches wide, inclining backwards at an angle of about 45^ to 

 the plane of the lateral margin. Dorsal valve gently concave, conforming 

 in its curvature to that of the ventral valve ; area half a line wide, form- 

 ing nearly a right angle with the ventral area. The muscular impressions 

 of the ventral valve are rather large, flabellate, extending from the beak 

 nearly half the length of the shell. The divaricators (in the only speci- 

 mens in which they have been seen) are divided into six or seven longi- 

 tudinal lobes, not distinctly defined at their anterior margins. The occlu- 

 sors occupy an elongate, narrow space, and seem to extend from near the 

 beak to near the front of the divaricators. There is a slightly elevated 

 mesial septum between the occlusors, one-half or two-thirds their length 

 from the beak. Hinge fine crenulated, apparently nearly out to the end» 

 Deltidium and internal characters of the dorsal valve unknown. 



Surface with coarse, flexuous, shghtly elevated, rounded, radiating 

 strioe, which increase, both by bifurcation and intercalation, four or five in 

 the width of two lines. When the surface of the shell is perfect, it exhi-- 

 bits a set of fine but very distinct concentric striae, six or seven in the width 

 of one line. When partially exfoliated these become obscure, or disappear 

 altogether. The shell is not punctate. 



