Silurian Fossils 
93 
Spirifer swallowensis. 
j {Plate II, Fig. S 3 -) 
I Resembles Spirifer crispatus, but, in addition to the median 
! fold of the brachial valve and the two plications forming the sides 
j of the median sinus on the pedicel valve, there is on each side only 
one well developed lateral plication in place of two as in the case 
of Sp. crispatus, and the concentric lamellae appear coarser. 
Length, 11.5 mm.; width, about 14 mm.; thickness, 9.5 mm. 
Waldron bed: Swallow Bluff, north of landing, Tennessee. 
Atrypa reticularis-newsomensis, var. nov. 
{Plate I, Figs. ll A, B.) 
The assigning of a distinct name to this very common form of 
Atrypa reticularis is due merely to the convenience which a distinct 
; name offers when it is desired to record in the field the particular 
I variety which is present at any locality. It is not expected that 
this name will find general use. Radiating plications coarse, 8 
or 9 in a width of 10 mm. Shell of medium size. Types from 
Waldron bed at Newsom, Tennessee. 
Atrypa reticularis-niagarensis was figured by Nettelroth in Fos- 
sil shells of the Silurian and Devonian rocks of Kentucky, 1889, 
plate 32. There are from 12 to 14 plications in a width of 10 mm. 
The form of the shell is more variable than the figures by Nettel- 
roth suggest. It is the form figured by Roemer, fig. 9, plate 5, in 
his work on the Silurian Fossils of Western Tennessee. 
Atrypa arctostriata. 
{Plate II, Figs. 34 A, B.) 
Probably only one of the many varieties of Atrypa reticularis but 
apparently more distinct than the greater number of these forms. 
About 28 radiating plications in a width of lo mm. Fimbriate 
margin at different stages of growth well preserved. Shell of only 
moderate convexity, a specimen 15.5 mm. long and 18.5 mm. wide 
having a vertical dimension of only 7.5 mm. 
Brownsport bed; glade southwest of Brownsport Furnace, 
three miles west of Vice landing, Tennessee. 
