84 
PALJEONTOLOSY OF NEW-YORK. 
473. 7. AYICULA RHOMBOIDEA (n. xp.). 
Pl, XXVII. Fig. 2 a, b, c, d. 
Shell rhomboidal, higher than long; hinge-line nearly straight, or slightly deflected ; base 
rounded ; sides nearly parallel, and slightly sinuous; beak prominent, and a little elevated 
above the cardinal margin ; umbo prominent, becoming gradually depressed towards the mar¬ 
gin ; anterior wing short, rounded, and separated from the central part of the shell by a sinus ; 
anterior wing triangular, not extending so far as the posterior margin of the shell; surface 
marked by concentric striae, which become, at intervals, prominent folds indicating stages of 
growth. 
In young specimens the beak is usually more sharply defined, the umbo more prominent, 
and sometimes the posterior wing is very acute. The specimens known occur mostly in sand¬ 
stone, so that little more than a cast is preserved. In these casts there is no evidence of longi¬ 
tudinal striae, and in a single specimen in shale there is likewise no evidence of such striae. 
In sandstone the specimens are very convex, and even gibbous, while the one in shale is 
extremely compressed, giving a slightly different aspect. 
Fig. 2 a. A large individual, in which the anterior wing is less prominent than usual. 
Fig. 2 b. A smaller specimen. 
Fig. 2 c. A young specimen, having the length nearly equal to the height. 
Fig. 2 d. The posterior portion of another specimen, having the striae more perfectly preserved 
and the angle of the wing more extended. 
Position and localities. In the fine-grained sandstones near the base of the grbup at Black- 
stone’s quarries, New-Hartford ; and in the upper green shale of the groupj associated with 
Chonetes, at Sodus, Wayne county. 
474. 19. MODIOLOPSIS SUBALATUS (n. sp.). 
Pl. XXVII. Fig. 5, and 6 a; b. 
General form ovate or sub-rhomboidal ; posterior side expanded and sub-alate ; umbo pro¬ 
minent, and the beak slightly elevated above the cardinal line • anterior side narrow, rounded 
or sub-acute; surface marked by fine equal concentric striae. 
This shell is usually of the size of those in fig. 5, of which considerable numbers occur at 
Rochester in the upper green shale, and particularly in a thin bahd of purple shale included in 
the former. It is associated with Atrypa hemispherica ; but from its small size and compressed 
condition it scarcely attracts attention. 
Fig 5. A fragment of slate, with figures of the right and left valve* 
Fig. 6 a , l. Figures of the right valve of two specimens of large size. The specimen fig. 6 a 
is somewhat crushed, and the figure gives an incorrect representation of its true 
character. 
