RAYMOND: ISOTELUS GIGAS DEKAY. 257 
Co., Iowa, has appeared. He describes and figures Isotelus cowensis 
from specimen obtained at the type locality. Mr. Slocum figures 
(Pl. 13, fig. 2) one remarkable specimen which has the appearance 
of possessing an epistome, and he has described the sutures as indi- 
cating the presence of this plate. Mr. Slocum was kind enough to 
show me this specimen, and while there are certain lines which have 
decidedly the appearance of epistomal sutures, I am unable to believe 
that this species has an epistome, that plate being entirely unknown 
among the Asaphidae. The facial suture is described by Slocum as 
marginal, but although it is nearly so, many specimens show clearly 
that it is intramarginal or “ Isoteliform.” 
The M. C. Z. contains two specimens from the Moquoketa of Iowa 
which show the doublure of the cephalon. Both show a median verti- 
‘eal suture such as is seen in all other Asaphidae and one of them 
(M. C. Z. No. 485) shows at the left a suture such as that on Mr. 
Slocum’s specimen. ‘There is no corresponding one on the right side, 
however, and the other specimen (M. C. Z. No. 442) shows no trace 
of such a suture on either side. Just what these lines indicate is not 
at present evident. 
IsOTELUS MAXIMUS Locke. 
Isotelus maximus Locke, Second ann. rept. Geol. surv. Ohio, 1838, p. 246, fig. 
8,9. Clarke, Pal. Minn., 1897, 3, pt. 2, p. 701 (not fig. 5-7). Raymond 
and Narraway, Ann. Carnegie mus., 1910 7, p. 55, fig. 3. 
Tsotelus megistos Locke, Trans. Amer. assoc. geol. and nat., 1841, p. 221, pl. 6; 
Amer. journ. sci., 1842, ser. 1 42, p. 366, pl. 3. Meek, Pal. Ohio, 1873, 
1, p. 157, pl. 14, fig. 13. Miller, Cincinnati quart. journ. sci., 1874, p. 137. 
Asaphus megistos Walcott, Science, 1884, 3, p. 200, fig. 1. 
_ Typical and well-preserved specimens of this species from about 
Cincinnati are very easily distinguished from specimens of Jsotelus 
gigas from Trenton Falls, or specimens of Isotelus iowensis from Iowa, 
but they are not always so easily separated from the other two species 
of Isotelus found with them at Cincinnati. The chief reason for the 
confusion which has arisen as to the characteristics of the two species, 
Isotelus gigas and I. maximus, is that five species, belonging to two 
genera, have been identified under these two names. At Cincinnati, 
the common asaphids are Isotelus gigas, I. maximus, I. latus, and un- 
described species of Isotelus and of Onchometopus. At Trenton Falls 
the only species are Isotelus gigas and I. iowensis, but the I. iowensis 
