182 2'he American Geoloyisf. March, 1897 
occur on both continents. The follow! nji; are the species from 
the Galena and Maquoketa series: 
1. I^lectamboiiites sericea (Sowerbj^). Siluria, pi. 19, f. 1, 
(1839); Davidson, Silurian Brachiopoda, p. 323, pi. 48. tig. 
10-19, (1871), is probably the same as the first of our forms in 
the Galena series. It has been so identified by Hall, Pal. N.Y., 
vol. 8, pt. 1, pi. 15, f. 25-29, (1894); vol. 1, p. 110, pi. 31. B. f. 
2 (1847), although the figures by the English authors repre- 
sent the dorsal muscle scars difi'erently from our specimens. 
This species is found in the Stictoporella bed (3) and in the 
top of the Stictopora bed (4), and abundantly in the Fucoid 
l)ed (5) of the Galena series. 
2. /'. mi niiesof east's (Sardeson). Bull. Minn. Acad. Nat. 
Sci., vol. 3, p. 329, pi. 6, fig. 24-25 (1892), is very abundant in 
the Orthisina bed (6), rarer in the Camarella bed (7). 
3. P. (jibbosa Winchell and Schuchert, final rep., vol. 3, 
Geol. Nat. Hist. Sur. Minnesota, p. 416. pi. 32, f. 13-17 (1893) 
is known from the Lingulelasma bed (8), in Minnesota only. 
4. J'iectambonites Q.L serioea. A few ventral valves of a 
large species are associated with the last in the upper part of 
the bed, in Dodge county, Minnesota. 
5. P. pra-cosis (Sardeson), loc. cit., p. 329, pi. 4, f. 26-28, 
is abundant in the Triplicia bed (10) of the Maquoketa 
series. 
6. P. soxea (Sardeson), loc, cit., p. 330, pi. 4, f. 33-35. is 
known in Minnesot i and Iowa in the Orthoceras bed (12). 
P. recedeus (Sardeson) loc. cit, p. 330, pi. 4, f. 29-32 (1892). 
P. sericea W. and S., (non Sow. ?) loc. cit., p. 414, pi. 32, fig. 
12, 10-U, (1893); LepUvna sericea ? Meek, Pal. Ohio, vol. 1, 
p. 70, pi. 5, fig. 3 a-e, notf-h, (1873), is common in the Leptfv.na 
bed (13), and Orthis bed (14), of the Maquoketa series, and is 
the same, apparently, as found in the upper part of the Cin- 
cinnati shales in Ohio. 
These species follow closely upon one another in the strata, 
and if phylogenetically successive varieties of the same spe- 
cies be interpreted from their relationships, it remains, never- 
theless, evident that the transitions are wanting, as in Orthis 
festudinaria auct. In the lower Cincinnati shales of Ohio 
there is still another species, Plectambonites asjoera (James) 
Cincinnati Q. J. Sci., vol. 1, p. 151 (1874); Leptana sericea 
