TRILOBITES. 701 
Tsotelus gigas—maximus.] 
is subserved in the retention of this name. For purposes of comparison a copy of 
Dalman’s figure of Asaphus expansus is here introduced. 
Fig. 4. Outline of Asaphus expansus Wahlenberg (after Dalman). 
Isoretus aicas DeKay, 1824. 
Isotelus gigas DEK AY, 1824. Annals Lyceum Nat. Hist. N. Y., vol.i, p. 174, pl. 12, fig. 1, pl. 13, fig. 1. 
Asaphus platycephalus (STOKES) of most authors. 
IsoreLus maximus Locke, 1838. 
Isotelus maximus LOCKE, 1838. Second Ann. Rept., Geol. Surv. Ohio, p. 246, figs. 8, 9. 
Tsotelus megistos LOCKE, 1841. Trans. Amer. Assoc. Geol. and Nat. p. 221, pl. 6. 
Asaphus megistos (LOCKE) of most authors. 
In referring to these two widely known trilobites under the same caption, it is 
not the intention to assume their specific identity. Itis, however, on many accounts 
convenient to consider them together, as careful study of a large series of both forms 
has elicited some important suggestion concerning their mutual relations. 
The usual basis of distinction between these contemporaneous fossils is an 
exceedingly simple one. Constructed upon essentially the same specific type, the one, 
I. gigas, is devoid of cheek spines; the other, J. maximus, possesses them. It is hardly 
necessary here to enter into a detailed account of the characters of these fossils. 
They have been given at length by various authors, Hall,t Burmeister,? Meek,* 
Miller,* and others. 
In the original specimens the conventional distinction between the species was 
clearly indicated. DeKay’s figures, one of an enrolled example, one of an extended 
(1), Palawontology of New York, vol. i, p. 231; plates 60, 61, 62, 63, 1847. 
(2). Organization of the Trilobites (Ray Society’s translation), p, 110, pl. 2, fig. 12, 1843, 
(3). Palaeontology of Ohio, vol. i, p. 159, pl. 14, fig. 13, 1873. 
(4), Cincinnati Quart. Journ. Science, vol, i, pp. 187, 138, 1874, 
