RAYMOND: ISOTELUS GIGAS DEKAY. 257 



Co., Iowa, has appeared. He describes and figures Isotelus iowensis 

 from specimen obtained at the type locality. Mr. Slocum figures 

 (PI. 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- 

 cal suture such as is seen in all other Asaphidae and one of them 

 (M. C. Z. No. 435) 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 rnaximns Locke, Second aiin. 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. 



Isotelus megisios Locke, Trans. Amer. assoc. geol. and nat., 1841-, p. 221, pi. 6; 

 Amer. journ. sci., 1842, ser. 1 42, p. 366, pi. 3. Meek, Pal. Ohio, 1873, 

 1, p. 157, pi. 14, fig. 13. Miller, Cmcinnati quart, journ. sci., 1874, p. 137. 



Asaphus megistos Walcott, Science, 1884, 3, p. 200, fig. 1. 



Typical and well-preserfed specimens of this species from about 

 Cincinnati are very easily distinguished from specimens of Isotelus 

 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 /. 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 Trentoii Falls 

 the only species are Isotelus gigas and /. iowensis, but the /. iowensis 



