238 NEW FOSSIL SHELLS 
FAMILY MACTRIDAE. 
GENUS ALIGENA, (Nosis.) 
Testa aquvalvis? subequilateralis, postice et anticé clausa; cardo dente cardinali uno, sulco sub natibus longo, minimé 
profundo, 
Shell equivalve? sub-equilateral, closed posteriorly and anteriorly; hinge with one cardinal tooth, and a long shal- 
low sulcation under the beaks. 
Remarks.—The cardinal tooth is, in general, rather small. The sulcus appears to 
have received the ligament. It commences at the beak, and runs obliquely past the 
dorsal margin into the cavity under the beak. As I possess only odd valves of both the 
following species, | am unable to determine whether the shell is equivalve or not. 
I have in vain endeavoured to find some genus, already described, which might receive 
these little shells, but their peculiar characters in having one cardinal tooth, and a liga- 
mentiferous sulcation, descending into the shell, distinguish them from other genera. 
Their place in the systems is, most probably, in the family Mactride, between Erycina 
and Ungulina. 
I have called the genus, Aligena, one of the surnames of Venus, from its resemblance 
to Erycina, also an appellation of that goddess. 
A. striata, Px. 34. Fie. 13. 
A. testi transversd, sub-ellipticd, posticé et antice rotwndatd, inflatd, tenui, striatd; striis concentricis, prope marginem 
basalem maximis; clivo umboniali elevato, sub-angulato; margine basali cwrvato; margine dorsali medio angulato, posticé et 
anticé curvato; natibus prominentibus, incurvis, sub-levibus; dente cardinali minimo; sulco longo, pene transverso; margine 
interno integro. 
Shell transverse, sub-elliptical, rounded anteriorly and posteriorly, inflated, thin, striate; strim concentric, very 
large near the basal margin; umbonial slope elevated, somewhat angulate; basal margin curved; dorsal margin angu- 
lar in the middle, curved posteriorly and anteriorly; beaks prominent, incurved, nearly smooth; cardinal tooth very 
small; suleation long, nearly transverse; margin entire within. 
Diam. .10, Length .19. Breadth .21 of an inch. 
Remarks.—The concentric strie are irregular in size and number, but there is a 
general increase from the beaks to the base. Those near the base, indeed, almost merit 
the name of coste. The cardinal tooth is extremely small. 
: mJ 
A. tmvis, Pi. 34. Fie. 14, 
A. testé transversd, sub-quadriiaterali, postice rotundatd, anticé subtruncatd, convexd, inflatd, levi; margine basali 
recto; margine dorsali medio angulato, postice et antice curvato; natibus sub-prominulis, incurvis; dente cardinali 
longo; sulco lato, curto, pené transverso; margine interno integro. 
Shell transverse, sub-quadrilateral, posteriorly rounded, anteriorly sub-truneate, convex, inflated, smooth; basal 
margin straight, dorsal margin angular in the middle, curved anteriorly and posteriorly; beaks somewhat prominent, 
inecurved ; cardinal tooth long; suleation wide, short, nearly transverse; margin entire within. 
Diam. .14. Length .18. Breadth .22 of an inch. 
Remarks.—There are a few, almost imperceptible lines of growth over the surface of 
the shell, which, under a powerful microscope, give it a somewhat roughened appearance. 
The cardinal tooth is very long, and the sulcus is shallow, so that the hinge, at first 
glance, is not unlike that of the genus Thracia. 
Ses 
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