253 



almost vertically-truncate posterior 

 end; well-marked angular umbo- 

 nal ridg'e; strong, even, unitV^rm. 

 angular concentric stria^. 



Found in the Encrinal limestone, 

 at Section 5 (very rare); nine to 

 twelve feet below the Encrinal 

 limestone, at Section 7 ; tA\'enty- 

 five feet below the Encrinal lime- 

 stone, in Idlewood Ravine; and in 

 the Pleurodictyum beds, and the shales just above, and 

 down to and in the Strophalosia bed, in Avery's Creek, and 

 on the Lake Shore. 



Fig. 169. Cypricardelln helli- 

 striata. A specimen retaining 

 both valves in conjunction ifrom 

 Hall). 



Genus XUCULA. La.m.aki k. 



[Ety. : XucuIh, a little nut.] 

 (1801: Syst. Au. Sau.s. Vert., p. ST.) 



"Shell small, ineijuilateral. trigonal or transversely ellip- 

 tical or sub-circular. Anterior or posterior extremity some- 

 times produced, usually rounded. Beaks anterior or 

 posterior to the middle of the length, often sub-central. 

 Cardinal line arcuate. Escutcheon marked. Surface marked 

 by concentric stride, which, in some species, are regular and 

 rugose. Hinge furnished with a. triangular, spoon-shaped 

 cartilage-pit beneath the beaks, with a series of small trans- 

 verse teeth on each side. There are two principal muscular 

 impressions on each valve, witli usually a smaller retractor 

 scar adjacent, and also the cavity of the beaks often shows 

 several pits for the attachment of umbonal muscles. Pallia! 

 line simple." (Hall, Pal. N. Y.. Vol. V., Pt. I., p. xxvi.) 



Xuci'LA C0Ri3Ui.iFOR.Mis. Hall. ( Fig. IGDA. ) (Pal. N. Y., 

 Vol. Y., Pt. L, p. 819, PL XLYl.) 



Distil] ffiiishinQ- Characters. — Broadlv trianaular. sub- 

 ovate outline ; length about one-fourth greater than height ; 

 longer, more pointed posterior end ; broad and slightly in- 

 curved beaks, from which the cardinal line declines in both 



