260 ARCIDA. 
angulate like Cucullzea; hinge with about four cardinal teeth in 
the right and five in the left valve. 
CrEeNopontaA, Salter, 1851. 
Syn.—Tellinomya, Hall. 
Distr.—Fossil, 40 sp. Silurian—Carboniferous; Europe, N. 
America, Bolivia. C. pectunculoides, Hall (exxvi, 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 differ by a more 
elongated and more tumid form. 
It is probable that most of the paleeozoic species referred to 
Nucula belong to Ctenodonta. 
TELLINOMYA, Hall, 1847. Has been considered a synonym of 
Ctenodonta; per haps some species referred to it really belong here. 
Many of the paleozoic genera are very difficult to classify, because 
they are frequently not well-preserved, and the essential char- 
acters are consequently wanting. ZT. nasuta, Hall. 35 sp. 
Sarepra, A. Adams, 1860. 
Distr.—S. speciosa, A. Ad. Japan. 
Shell oval, equivalve, not pearly within; hinge-line nearly 
straight, provided with numerous denticles, cartilage internal, 
below the beak; muscular impressions distant, pallial line entire. 
“This genus,” says the author, “agrees with Nucula in the 
simple pallial 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. 
CarpionaRtA, Munier-Chalmas, 1876. 
Distr. C. Barrandei, M.-C. Palzozoic; France. 
Shell equivalve, thin and subcircular, convex; hinge witha 
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. 
NucinE.ia, S. Wood, 1848. 
Syn.—Nuculina, d’Orb., 1844. Pleurodon, Wood, 1840. 
Distr.—Fossil. N. miliaris, d’Orb. (exxvii, 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 
