LAMELLIBRANCHIA TA. 
385 
EUTHYDESMA, n. g. 
Euthydesma subtextile. 
PLATE LXIII, FIGS. 11-16; AND PLATE XCIII, FIGS. 28,29. 
Astarte subtextilis, Mali.. Geol. Surv. N. Y., Rep. Fourth Dist., p. 245, fig. 6. 1843. 
Cardiomorpha subtextilis. Hall. Prelim. Notice Lamellibranchiata, 2, p. 93. 1870. 
“ “ “ ( texiilis , in error). Pal. N. Y., vol. v, pt. 1. Plates and Explanations: 
PL 63, figs. 11-15. 18S3. 
“ undulata, “ Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 63, fig. 16. 1883. 
Shell large ; body broadly sub-ovate, with a sub-alate cardinal expansion ; 
length one-fifth greater than the height; basal margin very regularly curv¬ 
ing to the post-inferior extremity, which is sub-truncate above. Cardinal 
line rigidly straight. Anterior end short and regularly rounded. 
Valves moderately convex in the posterior part, very gibbous in the mid¬ 
dle and umbonal region. 
Beaks sub-anterior, large, prominent and incurved. Umbonal slope rounded 
and merging into the general convexity of the shell. 
Surface marked by fine, sharp, elevated concentric striae, which, in well- 
preserved shells, are crossed by fine, slender, radiating striae, giving the sur¬ 
face a cancellated appearance. At the intersection of the striae, minute 
nodes are formed. In old shells the surface becomes raised into unequal 
concentric undulations and also into stronger undulations, which cross the 
lines of growth obliquely on the middle of the shell. Some specimens show 
two low plications along the post-cardinal slope. 
Hinge-line straight and marked by a distinct, continuous ligamental 
groove. Other characters of the interior unknown. 
Two specimens measure respectively 37 and 45 mm. in length, and 30 and 
37 mm. in height. The largest specimen observed has a length of about 
75 mm. 
A careful comparison of this fossil with other species shows it to be so 
entirely distinct in its form and exterior characters, as well as in the features 
of the hinge, that there are no allies in our geological formations with which it 
