60 C. F. Liitken on Ophiurans. 
in the arms, the number of joints with hooks on the under side 
and the number of joints without a circle of grains round the 
upper arm-plate are brought into immediate comparison. 
Joints without 
Diameter of disc. Length of arm. No, of joints. Joints with hooks. circle of grains. 
2mm, 6 mm, 20 15 12 
3 40 27 
4 45-50 33 20 
6 33 
10 60 86 
14 712 105 40-50 18 
According to this table both the disc and the arms continue 
to grow, but the latter the faster. During the growth of the 
arms new joints are formed, and this increase of joints seems 
greatest in the very | ey animal. The new joints appear at 
the tip of the arm and not at the base, next the mouth. 
Subdivisions of genus Ophiolepis (Mill. & Trosch.), 
This genus is thus described by its authors: “ Naked scales, or 
little shields, on the disc. Mouth-slits surrounded by a single 
row of hard papillz, without an increase of their number over 
tooth-columns.” It will presently appear, however, that 
the species included under this definition represent several gen- 
Following the suggestions of Forbes, it will be seen, that 
Ophiolepis includes two series of scaly Ophiurans, one answering 
in some sort to the type of Ophioderma, the other to that of 
Ophiocoma, as expressed in the following table. 
First Szrres—Type of Ophioderma. 
arm-plates. : 
Ophiura.—Disc covered with larger or smaller scales, smooth 
and naked radial shields tolerably large, protruding, more or less 
distinct. Incision in the disc limited by two arches curving out- 
wards, and admitting three to four imperfect upper arm-plates; 
on its edges a close crest of from ten to thirty papilla, which are 
continued underneath, along the edge of the genital opening, to 
the mouth-shield, Another more obscure crest of papilla lying 
under the first and running only a short distance. Mouth-sbields 
very large, generally longer than broad, shield-shaped, extending 
into the interbrachial spaces, thus separating the inner ends of the 
rape opening: ‘ the madreporic shields not differing in form. 
narrow, lying inside the mouth-shields prop- 
