SYNOPSIS OF GENERA. xxv 



Microdot!, Conrad (Journal of the Academy of Natural Sciences, Philadelphia, 

 vol. viii, p. 247. 1842). [Type, Microdon bellistriata, Conrad.] 



Shell equivalve, inequilateral, transversely sub-elliptical or sub-quadrate in 

 outline. Cardinal line straight or slightly arcuate. Anterior end narrowed 

 and rounded. Posterior extremity broad and truncate. Beaks small, pointed, 

 appressed, situated nearer the anterior end. Umbonal ridge more or less 

 defined, extending from the beaks to the post-inferior angle. 



Surface marked by more or less rugose and regular concentric striae. 



Hinge characterized by a triangular tooth in each valve, that of the left 

 valve short and situated beneath the beak, with a more elongate pit or groove 

 l)ehind it for the reception of the tooth of the right valve. The right valve 

 ha.s also a triangular pit beneath the beak for the reception of the short tooth 

 in the left valve, and a longer triangular fold behind, which is sometimes 

 double. No lateral teeth have been observed, unless the long oblique fold of the 

 right valve be regarded as a lateral tooth. Ligament external, extending almost 

 or quite the entire length of the cardinal line. Anterior muscular impression 

 moderately large, sub-circular or short reniform ; posterior scar superficial. 

 Pallial line simple. 



Owing to the fact that the name Microdon had previously been established by 

 Agiissiz for a genus of fishes, the name Eodon was proposed by Hall and Micro- 

 dondla by (Ehlert. The genus Cypricardella (Trans. Albany Inst., vol. iv. 

 1856) has been shown to be identical with Microdon* If the name Microdon 

 in to be suppressed, the name Cypricardella will have precedence. Microdon is 

 retained for the present, using the genus Cypricardella parenthetically. 



Examples : Microdon {Cypricardella) bellisiriatus, pi. Ixxiii, figs. 7-22 ; pi. 

 Ixxiv, figs. 5-10. 

 Microdon {Cypricardella) tenuistriatus, pi. Ixxiii, figs. 23-30; pi. 

 Lxxiv, tigs. 20, 21. 



• R. P. "Whitfield. Bull. Am. Mus. Nat. Hist., vol. i, No. 3, p. 63. 1882. 



