508 PALEONTOLOGY OF ILLINOIS. 



as the costre themselves, while its surface shows no traces of the fiuer 

 sculpturing seeu ou that shell. 



Position and locality : Grafton, Illinois ; from a light-drab maguesian 

 limestone of the age of the New York Niagara Group. Upper Silurian. 



CRUSTACEA. 



G-estjs LICHAS, Dalman. 



Lichas Boltoni, Bigsby (sp.) 



PI. 25, Pig. 5. 



Paradoxides Boltoni, Bicsbt, 1825. Jour. Acad. Nat. Sci., Philad., Vol. IV. p. 302. Greex, (1832,) 

 Mor.ogr., p. 6, PI. 1, fig. 5. Also, (1832) Monthly Am. Jonr. Geol., p. 3G0 ; Hablax (1834,) Trans. 

 Geol. Soc. Pa.. Vol. I, p. 103, and Aled. audPhys. Researches, p. 401. 



Platynotus Boltoni, Coxrad, 1838. Ann. Pep. Pateont.. N. V., p. 118; Hall Geol. Rep., Foorth 

 Dist., N. Y. 



Actinurus Boltoni, Castlexau, 1843. Ess. Snr. Sil. Syst,, de l'Amer. Sept., p. 21, t. 5, fig 3. 



Lichas Boltoni. Hall, 1852. Falcon t. X. Y., Vol. 2d., p. 311, PI. B9, 70, fig. 1 a, b, etc., (not It.) 



The only specimen of this species yet known to us from any Illinois 

 locality, consists of the pygidium, in a tolerable good state of preserva- 

 tion. It agrees with the New York species too nearly, we think, to be 

 regarded as a distinct species, though we can see some slight differences 

 in its details. For instance, the anterior end of its mesial lobe is more 

 convex than that of any New York specimens we have seen, but as the 

 latter are all in soft shale, it is probable this difference may have been 

 produced by pressure. The angular projections of its posterior margin 

 are also rather more pointed than is usual in New York examples. In 

 these characters, and its rather distinctly and coarsely granular surface, 

 it seems to agree well with a form described by Prof. Hall under the 

 name L. Boltoni var. Occidentalis, from TTaldron, Indiana, but as we 

 have seen no figure, and but a brief description of that type, we cannot 

 be sure of the identity of our specimen with it. 



Position and locality : Niagara Group, of the Upper Silurian. Graf- 

 ton, Illinois. 



Genus ILLE2\ t US, Dalman. 

 Ill^ntjs (Bumastus) Graftonensis, M. and W. 



PI. 25, Fig. 4. 

 lllcenus (Bumaislus) Graftonensis, Meek and Womhex, 1869. Proceed. Acad. Nat Sci., Philad. 



Attaining a rather large size. Head (determined from internal cast) 

 transversely subelliptic as seen from above, when placed with the under 



