ASTARTID^. 231 



the margins, thin in the middle, on the surface concentrically stri- 

 ated or lamellated ; ligament external, vei'y long ; muscular impres- 

 sions rather large, the anterior close to the hinge and with a 

 small superimposed impression; pallial line entire, hinge un- 

 known. A. intrepida^ Dana (cxxii, 14 \ Carb. ; N. S. Wales. 

 This group is based upon a number of carboniferous species 

 from New South Wales ; they greatl}' resemble in external form 

 the subgenus Caryatis of Cytherea, but the long ligament and 

 muscular impressions appear to be very similar to those of 

 Astarte. The examination of the hinge-teeth is required for the 

 correct determination of the family to which these shells belong. 



Mecynodon, Keferstein, 1857. 



Distr. — Devon. ; Eur. M. carinatas, Goldfuss (cxxii, 42, 43). 



Shell rather long, thin, concentrically striated or smooth, with 

 a diagonal keel, extending from the beak to the posterior margin ; 

 ligament external, short ; hinge in either valve with an elevated, 

 long tooth parallel with the hinge-margin, and a pit, posterior 

 to the tooth in the right valve, and anterior to it in the left, in 

 both valves a long and stout posterior lateral tooth ; anterior 

 muscular impression deep, with a smaller but deeper impression 

 of the foot-retractor behind it ; posterior impression near the 

 middle of the posterior margin. 



Subfamily GARDITINjE. 



Shells roundl}^ ovate or transversely elongated, always pro- 

 vided with radiating ribs or striae. 



Cardita, Bruguiere, 1189. 



Etym. — Gardia^ the heart. 



Syn. — Arcinella, Oken. Pseudocardia, Yetocardia, Conrad. 

 Actinobolus, Klein, 1753. 



Distr. — 50 sp. Universal. Fossil, 5 sp. Lower Silurian — 

 Trias ; United States, Europe, New South Wales, Tasmania. G. 

 sulcata., Lam. (cxxiii, 67). G. antiquata, Linn, (cxxiii, 68). 



Shell oblong, radiately ribbed ; ligament external ; margins 

 toothed; hinge-teeth 12, and an elongated posterior tooth; 

 pallial line simple ; anterior pedal scar close to adductor. 



Animal with the mantle-lobes free, except between the siphonal 

 orifices ; branchial margin with conspicuous cirri ; foot rounded 

 and grooved, spinning a byssus ; labial palpi short, triangular, 

 plaited ; gills rounded in front, tapering behind, and united 

 together, the outer pair narrowest. 



REDONIA, Rouault. Shell oval, tumid ; hinge with cardinal 

 and posterior teeth ; anterior adductor bounded by a ridge. 

 Fossil. Lower Silurian ; Brittany, Portugal. G. Deshayesiana, 

 Rouault (cxxii, 47, 48). 



