1895.] NEW YORK ACADEMY OF SCIENCES. 125 
lus. Further, there is a ridge corresponding to the median 
ridge of the latter species, and also vascular lines similar in po- 
sition and direction. It is to be noted also that the position 
and general form of the posterior adductor aud lateral adjustor 
scar, of the ventral valve in both genera, are the same. There 
is, however, a marked difference in the position of the pedicle 
aperture in those two genera.. 
Additional examples of this species were found and show the 
surface ornamentation, consisting of numerous concentric ridg- 
lets, some more prominent than others; the radiating lines are 
faint and obscure, often not discernible. 
Horizon and locality. From the same horizon as those first 
found, viz., the middle of Assise 2. 
OBOLELLA, Billings. 
OBOLELLA NITIDA, Ford.? PI. ii., figs. 8 a and 5. 
Am. Jour. Sci., 3d Ser., vol. v., p. 213. 
U. 8. Geol. Surv. Bull., 30, p. 118, p. xi., fig. 2. 
Among the species of Obolella this little one appears only to 
be known from the figure and description by 8. W. Ford. We 
have found a few examples of a shell which does not appear to 
differ from this species. It would appear that Ford only had 
the dorsal valve, recognizable by the strong groove on the me- 
dian line in the posterior half of the shell. 
The dorsal in the Canadian examples is ovate-orbicular with a 
blunt umbo. There are impressions of the scars of the crescent 
that show through the shell, and traces also of the central group 
of muscle-scars. 
Sculpture. This, as far as the surface is preserved, shows an 
ornamentation due to waving irregular ridges, rather than the 
regular cancellation described by Mr. Ford. 
Size. Length of ventral valve 35 mm.; width, 3 mm. Length 
and width of the dorsal valve, each 3 mm. 
Horizon and locality. Sandstone of Div. 1, Band}. Assise 
3 at Hanford Brook. Rather scarce. 
LINNARSSONIA, Walcott. 
LINNARSSONIA TRANSVERSA, Hartt. Pl. v., figs. 1 @ to ec 
and 2a toe 
Obolella transversa Hartt, Acad. Geol., 2. Ed., p. 644. 
Obolella transversa Walcott. U. 8. Geol. Surv. Bull. 10., p. 16., 
pl. i., fig. 5 and 5a. 
