128 



the middle, somewhat flattened at the cardinal angles. Beak scarcely 

 distinct from the cardinal edges, a httle depressed below the greatest 

 height of the shell, perforated by a well-defined circular aperture. Area 

 proportionally rather large, flat, nearly at right angles to the plane of the 

 lateral margins, slightly overhanging the hinge-line. Foramen apparently 

 as wide as it is high, closed by a convex deltidium. Dorsal valve flat, all 

 except the margin, which is curved to correspond with the ventral valve. 

 Surface with about 30 fine, but distinct, radiating striae, about one-half of 

 which reach the umbo ; the intervening flat spaces with much finer striae, 

 just visible to the naked eye. A small space on the umbo is smooth, and 

 much of the remainder of the shell covered with small irregular undulations. 



Width of a ventral valve, on the hinge-line, 7 lines ; length about 4 

 lines. Width of a dorsal valve of another specimen, 6 lines ; length 3i 

 lines. 



Of this species only two detached valves have been collected. It is 

 evidently closely allied to Leptcenu Loveni (De Verneuil, Bui. Creol. Soc. 

 France, 2d series, vol. v., p. 339, pi. 4, fig. 5), but is proportionally 

 broader, and differs greatly in the curvature of the valves, as may be 

 seen by the figures above given. L. Loveni has also a deep sinus in the 

 middle of the front half of the ventral valve, and a corresponding fold in 

 the dorsal. 



Locality and Formation. — The Jumpers, Anticosti. In Division 4, 

 Anticosti group, Middle Silurian. 



Collector. — J. Richardson. 



Strophomena imbrex. (Pander.) 



a b 



#■::? 



Pig. 106. 



Fig. 106. — Strophomena imbrex ?—a, Ventral valve ; b, side view of one of the 

 forms of this species. 



Memarks. — This species only difiers from Strophomena alternata in the 

 curvature of the valves and in the surface characters. The visceral disc 



