204 
AUG. F. FOERSTE 
crease to 10 or 11 in the same distance. Occasional specimens 
occur in which the number of pits at midlength of the shell, just 
before reaching the point of intercalation of additional rows of 
pits, may equal 7, or even 6 in a width of 2 mm. On closer 
examination, the concentric striae are found to be not strictly 
continuous. From 4 to 10 pits may form a continuous series 
in a lateral direction; then there is a slight jog, beyond which 
there is another continuous series of pits. Only a single specimen 
was found in which the pits of adjacent concentric rows alter- 
nated sufficiently to accord with the description and figure of 
Trematis ottawaensis Billings (Palaeozoic Fossils, 1865, p. 53, fig. 
58), from the Trenton limestone at Ottawa, Canada. 
The specimens here described occur in the top of the Plattin 
limestone at Conn^s Ford, Buford Cave, and at the Yeager 
locality. 
In Trematis punctostriata Hall, from the type horizon and 
locality, in the Saltillo (Trenton) limestone at Clifton, Tennessee, 
similar features are shown. Posteriorly the pits are small and 
distant, on an otherwise smooth surface, disappearing before 
reaching the beak. Anteriorly the pits are separated only by 
narrow radiating and concentric striae. The number of pits 
sometimes reaches 8 in a width of 2 mm. near midlength of the 
shell, increasing to 10 and 12 in the same width along the an- 
terior margin. The concentric arrangement of pits is continuous 
for distances including 4 to 10 pits, beyond which there is a 
slight jog, followed by another continuous series of pits. Alter- 
nation of pits belonging to adjacent rows, as described in Tre- 
matis ottawaensis, is confined to only three or four rows in those 
few cases where it was detected at all. 
15. Zygospira deflecta Hall 
Plate XXII, figs. 5 A, B 
Shells small, scarcely exceeding 3 mm. in length, character- 
ized by a broad and distinct median depression on the brachial 
valve, its entire width occupied by five radiating plications, the 
total number of plications on the valve usually equalling 17 to 
