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 Avith about 30 fine, but distinct, radiatmg stri?e, about one-half of 

 which reach the umbo ; the intervenmg 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 Leptcena Loveni (De Verneuil, Bui. G-eol. 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.) 



Fig. 106. 



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

 forms of this species. 



Remarks. — This species only differs from Strophomena alternata in the 

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



