126 
PALAEONTOLOGY OF NEW YORK. 
their greatest width where they unite. From their 
line of union there is a short, acute and simple 
process extended horizontally backward. The 
attitude of the loop is erect, extending slightly back¬ 
ward at its base and then curving broadly forward 
Fig. no. hoo\) of Trematospira muUistriata, 
and upward; in height, it reaches rather more than iiaii. (c.) 
half-way across the bases of the spiral cones. The cones are situated as in 
allied genera, and the ribbon in mature shells, makes nine or ten volutions. 
Muscular impressions indistinct. Shell substance punctate. 
Type, Spirifer multistria.tus, Hall, Lower Helderberg group. 
Observations. Trematospira is well characterized in external features by its 
peculiar transverse form and general spiriferoid aspect; none of the allied 
genera can be confounded with it in these respects. Internally the structure 
of the hinge-plate and loop, the character of the muscular area and the nature 
of the articulation are all peculiar. The name Trematospira was proposed 
for a series of species occurring in the Lower Helderberg fauna, some of which 
had been previously referred to the genus Spirifer. At the time of the 
description of the genus no particular form was specified as the type, but 
among the typical species the first mentioned was T. multistriata, Hall, although 
the first in the descriptive list is T. perforata, Hall.* The former is taken as 
the typical species, as it is better known and of more frequent occurrence; 
T. perforata appears to be congeneric in all respects. 
The development of the Trematospiras in the Lower Helderberg fauna is 
remarkable; we have in the New York fauna, T. multistriata, T. perforata, 
T. costata, T. simplex. Hall, and from the Lower-upper Helderberg fauna at 
Square Lake, Maine, T. duhia, T. Hippolyte and T. Maria, Billings. In other 
faunas the genus is of rare occurrence. The Atrypa camura. Hall, of the 
Niagara group {Trematospira camura. Hall, 1859), is a small species which is 
probably the earliest representative of the genus, as it is doubtful if the still 
earlier form, described as Retzia {Trematospira) granulifera, Meek,f of the 
* PaliEontolog'y of New York, vol. iii, p. 208. 
t Palieontology of Ohio, vol. i, p. 128, pi. xi, fig. 6. 
