1036 DB. J. w. QBEaonT on thb CLASsiriOATioN [Dec. 15, 



reception of the podia. The adamhulacral ossicles have a flat 

 base, and thence bend forward crescentically. The mouth-frames 

 are massive, and those of each pair meet along the middle line of 

 the oral angle. 



Distribution. — Hamilton Series, Middle Devonian, Madeaon 

 County, New York. 



Type species. — Eugaster logani, Hall. 



Bemarlis. — This genus I only know from Prof. Jas. Hall's 

 figures, and in spite of their clearness I feel much doubt as to the 

 wisdom of diagnosing . it from these alone. Its affinities are 

 clearly with the Palseophiuridse, but it approaches the ProtasteridsB 

 in one respect : for, owing to the deep depressions in the outer 

 angles of the ambulacral ossicles, the outer side forms a short 

 rudimentary wing. The genus differs from all the Protasteridae 

 by the absence of a muscular groove across the ambulacral ossicles. 

 ' Among the Palseophiuridaj it differs from Palceopliiura by the 

 absence of marginal ossicles, and from Sturizura and Tceniura by 

 the massive nature of the mouth-frames. 



Genus 5. Ptilonastee, Hall, 1867. 



Distribution. — Chemung Series, Upper Devonian, Cortlandville, 

 New York State. 



Type species. — Ptilonaster princeps, Hall, 1867 [6. p. 292, pi. ix, 

 fig. 9]. 



Bemarlcs. — This genus is an ally of Eugaster, as Liitken [9. 

 pt. iii. p. 82] has already remarked ; it is, however, generically 

 distinct. I only know it from Hall's figures, and therefore prefer 

 to leave the preparation of a formal diagnosis to an American 

 palaBontologist. 



Order II. STEEPTOPHIUR^, Bell, 1892. 



Diagnosis. — Ophiuroida in which the ambulacral ossicles are 

 opposite and are generally fused into vertebral ossicles. In such 

 cases the vertebral ossicles articulate by a more or less simple ball- 

 and-socket joint. The covering-plates of the arms are more or 

 less regularly developed, and consist of a superior, an inferior, and 

 a pair of lateral arm-plates to each segment. The lateral arm- 

 plates generally bear spines. 



Bemarlcs. — The main character of this order is that the ambu- 

 lacral ossicles are paired, but primitive. The order differs from 

 the preceding by having the vertebral ossicles always opposite 

 instead of alternate. In some of the simplest mejnbers of the 

 order, as Ophiurina, the ossicles are not fused, there are no ventral 

 arm-shields, and an ambulacral furrow runs along the ventral side of 

 the arm. In the next higher family, as in the genus LapivoriJiura, 

 the ambulacral ossicles are fused, but have plain articulating 

 surfaces, and there is an ambulacral furrow. In recent members 

 of the group the vertebral ossicles are of a more complex type, but 

 the articulating surfaces are streplospondyline ; in some, such as 



