304 ARTHRODIRA, , / 
^ £**/./>' y,y-S' f-«, r7- 
1889), p. 44 : Macropetalichthys rapheidolabis\ Norwood 
and Owen, Amer. Journ. Sci. [2] vol. i. (1846), p. 371: 
Agassichthys sullivanti and A. mannx , J. S. Newberry, Bull. 
National Institute, 1857, p. 3 : Macropetalichthys manni , 
J. S. Newberry, Amer. Journ. Sei. [2] vol. xxiv. (1862), 
p. 75.—Corniferous Limestone (Lower Devonian); Ohio, 
[The type species; E. D. Cope Collection, Philadelphia.] 
Tf) ps b-tn* e d N • L L rvt v’ tf\. iSS$WH'. 
Genus HOMOSTEUS, Asmuss. 
[Das vollkommenste Hautskelet der bisher bekannten Thierreihe 
(Inaug. Dissert. Dorpat, 1856), p. 8 (Homostius).] 
Syn. Asterolepis, L. Agassiz ( non Eichwald), Poiss. Foss. Y. G. It. 
1845, p. 89 (in part) ; H. Miller ( non Eichwald), Footprints of 
the Creator, 1849, p. 70 (in part). 
Head and trunk broad, the dorsal aspect flattened ; scutes orna¬ 
mented with stellate tubercles; caudal region destitute of armour. 
Occipital elements of cranial shield constituting more than half of 
its length ; orbits completely surrounded, the preorbital and post¬ 
orbital plates forming the narrow outer bar ; a distinct small median 
bone over the pineal region, not perforated ; mandibular rami sutur- 
ally united at the symphysis, apparently toothless. A single broad 
median dorsal shield upon the trunk, with an inner longitudinal 
keel, and obtuse posteriorly ; two dorso-lateral plates on each side, 
the anterior relatively large, with a well-developed, forwardly- 
directed, antero-external process, but no prominent condyle for arti¬ 
culation with the external occipitals. [Ventral armour unknown.] 
The known species of this genus attain a large size, the width of 
the body-shield in H. milled being not less than 0*28. 
Homosteus formosissimus, Asmuss. 
1844. Asterolepis, L. Agassiz ( non Eichwald), Poiss. Foss. V. G. It. 
p. 96, pi. xxxii. figs. 2, 9, 10. 
1856. Homostius fopmosissimus, II. Asmuss, Das vollkommenste Haut¬ 
skelet der bisher bekannten Thierreihe, p. 35. 
1856. Homostius cataphractus, H. Asmuss, ibid. p. 36. [Median occi¬ 
pital ; University Museum, Dorpat.] 
1856. Homostius latus, H. Asmuss, ibid. p. 36. [Ditto.] 
1856. Homostius ponderosus, II. Asmuss, ibid. p. 37. [Lateral occipital; 
University Museum, Dorpat.] 
1856. Homostius anceps , H. Asmuss, ibid. p. 39. [Bones ; University 
Museum, Dorpat.] 
1857. Homostius, C. II. Pander, Placoderm. devon. Svst. p. 74, pi. viii. 
figs. 2, 6, 7. 
