368 THE PALEONTOLOGY OF MINNESOTA. 
[Treriiatis huronensis. 
" Shell-substance composed of an outer calcareous layer with a series of inner 
corneous lamellae. The outer layer varies in thickness in different species and is 
coarsely punctated by the pittings constituting the surface ornamentation. The 
corneous layers are irapunctate." (Hall, op. cit.) 
Type : Trematis terminalis Sharpe (not Emmons)=T. niillepunctata Hall. 
Trematis huronensis Billhujs? 
Fig. 29. Billings' original figure of T. huronensis. a, lower valve. 6, longitudinal section, showing 
the curvature of both valves; c, a portion of the surface enlarged. 
1862. Trematis huronensis Billings. Palaiozoic Fossils, vol. i, p. 53, flgs. 59a, 596, 59c. 
1863. Trematis huronenis Billings. Geology of Canada, p. 159, tigs. 130a, 130c. 
1892. Productella minneapoZis Saiideson. Bulletin of the Minnesota Academy of Natural Sciences, 
vol. iii, p. 332, pi. iv, flgs. 11, 12. 
Of Trematis we have seen but four imperfect specimens. Since they preserve only 
the dorsal valve, no direct comparison can be made with the ventral valve of T. huron- 
ensis Billings, and therefore this identification is provisional. The surface pittings 
in these specimens are similar to those in T. huronensis, i. e, they are arranged in 
radiating lines, not in quincunx, and in this respect differ from T. terminalis Emmons, 
T. inillepunctata Hall, and T. quincuncialis Miller and Dyer. Our specimens vary 
somewhat from Billings' species, in that the radial surface depressions become 
obsolete towards the anterior margin. 
The "ventral valves" of Productella minneapolis Sardeson are identical with the 
upper or dorsal valve of the shells identified by the writers with Trematis huronensis. 
Moreover, Productella is not known below the Devonian. 
Formation and locality. — From the Trenton limestone in the quarries along the river bluffs, and 
near the base of the Trenton shales at Minneapolis, Minnesota. The Canadian specimens are from the 
Black River limestone of Pallideau islands, lake Huron. 
Collectors.— G. L. Herrick and C. Schuchert. 
Mus. Reg. No. 7691. 
