260 ARCIDiE. 



angulate like Cucullsea ; hinge with about four cardinal teeth in 

 the right and five in the left valve. 



Ctenodonta, Salter, 1851. 



Syn. — Tellinomya, Hall. 



Distr. — Fossil, 40 sp. Silurian — Carboniferous ; Europe, N. 

 America, Bolivia. C. pectunculoides^ Hall (cxxvi, 30). 



Shell elongately oval, subequilateral, smooth, or finely concen- 

 trically striate, valves moderately convex, hinge represented by 

 two diverging comb-like denticulated margins without a special 

 hinge-area between them and the beak, and below the latter, not 

 interrupted by a pit ; ligament apparently external, posterior to 

 the beak. 



From Malletia the shells would seem only to difi'er by a more 

 elongated and more tumid form. 



It is probable that most of the palaeozoic species referred to 

 Nucula belong to Ctenodonta. 



TELLINOMYA, Hall, 1847. Has been considered a synonym of 

 Ctenodonta ; perhaps some species referred to itreall}^ belong here. 

 Many of the palaeozoic genera are very difficult to classify, because 

 they are frequently not well-preserved, and the essential char- 

 acters are consequently wanting. T. nasuta, Hall. 35 sp. 



Sarepta, a. Adams, 1860. 



Distr. — S. speciosa, A. Ad. Japan. 



Shell oval, equivalve, not pearly within ; hinge-line nearly 

 sti-aight, provided with numerous denticles, cartilage internal, 

 below the beak ; muscular impressions distant, pallial line entire. 



"This genus," sa3-s the author, " agrees with Nucula in the 

 simple pailial line and internal ligament, and with Malletia in 

 not being nacreous or pearly within, and in general form and 

 character." Is possibly a recent representative of the fossil genus 

 Ctenodonta. 



Cardiol ARIA, Munier-Chalmas, 1876. 



Distr. — G. Barrandei,M.-C. Palaeozoic; France. 



Shell equivalve, thin and subcircular, convex ; hinge with a 

 series of teeth similar to Nucula, the posterior ones the smallest 

 and most numerous ; pallial line simple ; anterior muscular im- 

 pression more developed than the posterior. 



NuciNELLA, S. Wood, 1848. 



/Syn.— Nuculina, d'Orb., 1844. Pleurodon, Wood, 1840. 



Distr. — Fossil. N. miliaris, d'Orb. (cxxvii, 78). 



Shell oval or subtrigonal, equivalve, inequilateral ; hinge wide 

 and curved, with sparse transverse teeth, and a long lateral tooth 

 on the longer anterior side ; muscular impressions unequal, the 



