282 Tlie American Geologist. May, i89o 
Fig. 9. Modiolopsis parva, n. sp. a, left valve X2.5, with the anter- 
ior end a little longer than usual, b, and c. cardinal and end profiles 
of same. Trenton group near Burgin, Ky. d, a left valve from the 
lower beds of the Cincinnati group at Covington, Ky., also X2.5, e and 
/", end cardinal profiles of same. The minute radiating stria) which 
occur on the posterior half of well preserved specimens are not shown. 
Shell very small, obliquely subovate and somewhat Avicu' 
loid in outline, much the widest posteriorly; greatest hight 
and length, respectively, as three is to five. Valves strongly 
convex, with point of greatest convexity above the center. 
Anterior end small, apparently not contracted in front of the 
beaks, narrowly rounded and often subangular at the anterior 
extremity of the hinge line. Central portion of basal margin 
straight, with the curves at the ends, where it rounds up into 
the anterior and posterior margins, equal. Posterior margin 
broadly rounded, the upper portion nearly parallel with the 
basal margin and formipg an angle of about 140° with the 
cardinal line. Hinge line straight, extending nearly to the an- 
terior extremity of the shell. Beaks small, nearly one-third of 
the length of the hinge from the anterior end. Umbones 
prominent, the umbonal ridge strongly rounded, extending 
to a point a short distance behind the center of the valve 
where it becomes obsolete. Cardinal slope flattened or slight- 
ly concave. Surface smooth or marked with obscure, irregu- 
lar, concentric furrows or striae, scarcely traceable in the car- 
dinal and posterior regions, where good shells exhibit instead 
exceedingly fine and crowded radiating striffi. Shell substance 
comparatively thick. Interior not observed. 
Greatest length of the largest specimen seen, 12 mm, ; length 
of hinge line, 8 mm. ; greatest hight measuring across the shell 
at right angles with the hinge line, from itsposterior extremity, 
8mm. ; distance from same point to center of basal margin, 7 
mm. ; greatest convexity of single valve, 2.5 mm. In a smaller 
example from the "Modiolopsis bed" of the Trenton of central 
Kentucky, the same series of measurements give, respective- 
ly, 9, 6, 5.7, 5, and 2 mm. 
The small size, straight hinge, Aviculoid outline, great con- 
vexity, and comparatively thick shell are the distinguishing 
features of this species, JI. alata, of this paper, bears some 
resemblance to it, but is a much less ventricose and more 
delicate shell. 
Position and locality : The original specimens are from the Cincin- 
nati group at Covington, Ky., where they were found at an elevation of 
