126 PALEONTOLOGY 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. 110. Loop ol' Trematospira mitlHstruita^ 



and upward ; in height, it reaches rather more than iiaii. ic ) 



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 multistriatus, 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 launa, T. multistriata, T. perforata, 

 T. costata, T. simplex, Hall, and from the Lower-upper Helderberg fauna at 

 Square Lake, Maine, T. dubia, T. Hippolyte and T. Maria, Billings. In other 

 faunas the genus is of rare occurrence. The Atrijpa 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 



* Palaeontolog'y of New Yoi-k, vol. iii, p. 208. 



t Palteontolof^y of Ohio, vol. i, p. 128, pi. xi, fig. 6. 



