<>KI>KK III 



TELEODESMACEA 



407 



_ 



TanentHa 



""/") <""> ""<, Zitt. 

 nd Qoi& Coral- 

 Rag ; Glos, Calvados. 



Family 15. Tancrediidae. Fischer. 



Shell Donaciform, equivalve, icith an external ligament; the margin of the valves 

 entire; hinge with posterior 

 mnl <uiterior laterals, the latter 

 inconstant ; cardinals one in 

 flu- left or two in the right 

 valve, or two in each valve. 

 Trias and Cretaceous, ? Recent. 



Tancredia, Lycett (Hettiut- 



gia, Terq. ; Palaeomya, Zitt. VTO /^r^j 



and Goub), (Figs. 737, 738). - 1 

 Shell sub- arcuate, attenuated 



lipfnrp flip Vipal-e wirlpr nnrl 



beaks, WICt y,-, ,,,/, ,rr (( ri/onm, Dunker sp. Lower 



shorter behind them ; obliquely Lias ; Hettingen, Lorraine. 1/1 (after Terquem). 

 truncate and somewhat gaping 



posteriorly ; a cardinal tooth on each side, and also an elongated posterior lateral. 

 Trias to Cretaceous ; maximum in Lias. 



? Meekia, Gabb. Cretaceous ; California. ? Hemidonax, Morch (Donacicardium, 

 Vest). Recent. 



Family 16. Unicardiidae. Fischer. 



Shell cordiform, equivalve, closed, concentrically striated; adductor scars elliptical, 

 the anterior longer ; pallial line simple ; margin of 

 the valve smooth ; ligament external, parivincular, seated 

 in a groove; with a grooved hinge plate bearing a single 

 obsolete cardinal in each valve, or none. Carboniferous to 

 Cretaceous. 



Unicardium, d'Orb. (Fig. 740). Rounded, inflated, 

 with incurved beaks ; hinge margin thin, with a weak 

 cardinal tooth; ligament deep-seated. Trias to Cre- 

 taceous. 



Scaldia, Ryckholt. Carboniferous. 



Pseudedmondia, Fischer. Ligament completely external. 



FIG. 740. 

 Unicardium excentricum, d'Orb. 



Kimmeridgian ; Cap de la Heve, ~ , . f 

 npnr Havre, i/,. Carbonitei'OTis. 



Family 17. Lucinidae. Fleming. 



Shell substance porcellanous or chalky, usually with inconspicuous or dehiscent 

 epidermis, rounded, variably sculptured ; valves equal, free, closed, with low, prosocoelous 

 beaks; adductor and pedal scars adjacent or distinct, the latter small; anterior adductor 

 elongated, largely within the pallial line, which is not sinuate ; area within the pallial line 

 often granular or punctate ; cardinal area small, often deeply impressed ; ligament and 

 resilium sub-internal, set in a deep groove, but usually more or less visible externally ; 

 hinge plate distinct ; lateral laminae distant from the cardinals, anterior and posterior 

 in the right, with corresponding sockets in the left valve ; cardinal teeth radial, formula 



^Y^, the posterior tooth larger and often bifid, but any or all of the teeth may be obsolete 

 or absent. Silurian to Recent. 



Paracyclas, Hall. Rounded, thin-shelled, concentrically striated ; no lunule ; 

 hinge unknown. Devonian. 



