1036 DR. J. W. GREGORY ON THE CLASSIFICATION _[Dec. 15, 
reception of the podia. The adambulacral 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, Madeson 
County, New York. 
Type species.—Eugaster logani, Hall. 
Remarks.—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 Paleophiuride, but it approaches the Protasteridx 
in one respect: for, owing to the deep depressions in the outer 
angles of the ambulacral ossicies, the outer side forms a short 
rudimentary wing. The genus differs from all the Protasteride 
by the absence of a muscular groove across the ambulacral ossicles. 
Among the Paleophiuride it differs from Palwophiwra by the 
absence of marginal ossicles, and from Sturtzwra and Teniura by 
the massive nature of the mouth-frames. 
Genus 5. Prinonastsr, Hall, 1867. 
Distribution.—Chemung Series, Upper Devonian, Cortlandville, 
New York State. 
Type species.—Ptilonaster princeps, Hall, 1867 [6. p. 292, pl. ix. 
fig. 9]. 
Pa ane genus is an ally of Hugaster, 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 
palzontologist. 
Order II. STREPTOPHIURA, 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. 
Remarks.—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 members 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 Lapworthura, 
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 streptospondyline; in some, such as 
