310 PALEONTOLOGY OF NEW-YORK. 
370. 2. TROCHOLITES PLANORBIFORMIS. 
Pi. LXXXIV. Figs. 3 a, b, c, d, e, f. 
Trocholites planorbiformis. Conranp, Jour. Acad. Nat. Sciences, 1842, Vol. viii, pag. 274, pl. 17, fig. 1. 
Depressed, orbicular, or planorbiform; volutions about four or five, wider than deep ; 
apex profoundly and equally depressed on both sides; aperture lunate; section elliptical, 
with the inner side concave from the junction of the next volution; surface marked by 
obliquely transverse ridges, which bend backwards, forming a broad curve on the dorsal 
line, longitudinally striated with rounded lines. 
In all the specimens examined, the outer lamina of the shell is exfoliated, and the fine 
strie of the surface are destroyed. The character of the shell is much like that of T. am- 
monius, and I have been disposed to regard it as a variety of the same. But in specimens of 
that species from the Trenton limestone, I have rarely found the transverse and longitudinal 
ridges so strongly marked as in this specimen. The shell is always larger than the specimens 
of the Trenton limestone, but in other respects there are few important.differences ; and it 
presents no greater variety than is represented in the Lituttes cornuarietis, by Murcuison 
and pE VERNEUIL. 
Fig. 3 a. Figure of a specimen nearly entire. 
This figure is given from an imperfect specimen, the parts wanting being supplied from 
the figure of Mr. Conran, the original of which I have examined in the cabinet of the 
Academy of Natural Sciences, at Philadelphia. 
Fig. 3 b. Dorsal view of the same. 
Fig. 3c. Ventral view of a fragment, preserving part of the two outer volutions, showing the concave 
ventral side, and the position of the siphuncle. 
Fig. 3 d. A portion of the surface magnified. 
Fig. 3 e. A specimen crushed in a vertical direction ; a part of the outer volution retaining its form in 
a sufficient degree to identify the species, 
Fig. 3 f, Dorsal view of the same, showing the slightly arching septa upon the dorsal line, and a part 
of the outer chamber. 
Nearly all the specimens found in the Hudson-river group, in New-York, are crushed 
and distorted. The single perfect specimen known to me, with another less perfect, were 
obtained near Grimsby, Canada West, by Mr. Asumrap of Philadelphia. 
Position and locality. This species occurs in the central part of the group at Turin in 
Lewis county, Pulaski in Oswego county, and several other localities. The specimens from 
Canada are associated with other fossils peculiar to this group, leaving no doubt of their 
position. (State Collection.) 
