264 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
teriorly but barely perceptible or obsolete in the front half of the valve. Beak 
smooth. Umbonal region marked by obscure concentric lines and indefinite radii. 
Small spines numerous on all parts of the shell but confined to lamellae on the 
front two-thirds. 
Measurements in mm.— 
Length Width Thickness 
Holotype (pedicle valve) Toc y os. wee cee cee 8.3 6.8 2.0 
Paratype (pedicle valve 100635) ............-- 8.6 8.0 1.8 
(brachial valve 109636c) ........... 7.5 7.7 1.0 
“ Ga eke Se PTOGOSOb Lane iuy Jone 9.1 8.4 ee 
Types.—Holotype: 109636f; figured paratypes: 109635, 109636b,d,e,g; un- 
figured paratypes: 109636a,c,h-m. 
Horizon and locality——Arline formation in Tennessee: 4 mile southeast of 
Friendsville, Concord (T.V.A. 138-SW) Quadrangle. 
Discussion.—The external expression of this species is like that of Schizambon, 
but the two genera can be readily distinguished by the fact that the foramen of 
Siphonotreta does not produce a long growth groove but is confined to the umbo. 
No other species of Siphonotreta is known in these rocks to which S. americana 
can be compared, but S. tertia of the Canadian (Sarbach) of Alberta is similar. 
The latter species differs from the one described herein by the finely papillose 
exterior and the absence of strong concentric lines. 
Genus SCHIZAMBON Walcott, 1884 
Schizambon Watcott, U. S. Geol. Surv. Mon. 8, p. 69, 1884—HALt and CLarKE, Pal. New 
York, vol. 8, pt. 1, p. 113, 1893.—ULRIcH and Cooper, Geol. Soc. Amer. Special Pap. 13, 
p. 60, 1938. 
This is generally a rare or unusual genus in the rocks above the Cambrian, 
but in the Southern Appalachians and at the Rock Crossing of Hickory Creek 
in Criner Hills, Okla., it is fairly common. Although the collection studied for 
this monograph is probably larger than any other of this genus ever brought 
together, it is nevertheless quite inadequate for a detailed study of the interior 
characters of this peculiar brachiopod. Although a question mark has not been 
placed after the generic name of any of the species referred to Schizambon in 
this book, it is doubtful if any of them are congeneric with S. typica of the 
Pogonip (Goodwin) formation. All these species conform to the present generic 
description, but that is obviously inadequate. 
Several differences between the Cambrian and Lower Ordovician Schizambons 
on the one hand and the Post-Canadian ones on the other are easily observable. 
All the Marmor-Trenton species observed by the writer are 2 or 3 times larger 
than the earlier ones, and the ornamentation is more elaborate. Furthermore, 
as pointed out by Hall and Clarke, no long pedicle tube occurs on the inside of 
the genotype as it does in S. canadensis and in some of the species described 
herein. The beginnings of such a tube is shown in S. borealis Ulrich and Cooper. 
The few specimens of Post-Canadian Schizambon in the National Museum 
collection that show the internal surface or are impressions of that surface fail 
