from the Laas and Oolites. 43 
Ophioderma Griesbachii, Wright. PI. III. fig. 2 a, 6. 
Diagnosis.—Body-dise small, upper surface not exposed, under 
surface irregularly subpentagonal, formed of five pairs of heart- 
shaped plates ; rays long, slender, and awl-shaped, prolonged 
beneath into the centre of the body-disc ; inferior surface with 
median vertebrate-like elements, and lateral scutal plates in 
the form of oblique pyramidal pieces, which clasp the sides of 
the rays in an imbricated manner, and support at their ter- 
minal points short stout spmes ; mouth subpentagonal, sur- 
rounded by ten blunt spinous processes, formed by the deve- 
lopment of the first lateral scutal plates of the rays, where they 
join each other around the mouth. 
Diameter of the body-dise ths of an inch, length of the rays 
from the mouth-margin to their apex }4ths of an inch. 
Description.—This beautiful Brittle-star of the Oolitic sea was 
discovered by our friend the Rev. A. W. Griesbach, of Wollaston, 
and we owe to his kindness and liberality the series of exquisite 
specimens before us, by which we have been enabled to complete 
the description of this new fossil. The body-dise is small, con- 
sisting of five pairs of heart-shaped plates ; the union between the 
separate elements of the disc was very intimate, as it is only at 
one or two points that a suture is exhibited ; so close is the union, 
that in other specimens the body-dise seems to be formed of a 
single circular-element ; each pair of plates has a heart-shaped 
form, and the ray corresponding thereto stands out in bold relief 
from the under surface of the disc. In none of the specimens 
found is the upper surface of the disc exposed, and we know 
not with certainty what kind of ornamentation adorned its 
dorsal surface ; at one part, however, where a portion of one 
of the plates is weathered, we think we detected with our 
inch object-glass under the microscope, a series of small imbri- 
eated scales resting on the rock surface; the rays are long, 
slender, and gently tapering ; their under surface, the only one 
exposed, exhibits, Ist, a central element having an elongated 
form, which resembles the body of a fish’s vertebrz in miniature ; 
2nd, lateral elements more largely developed, consisting of tri- 
angular plates of a pyramidal form slightly twisted round, by 
which arrangement the apices of the pyramids are made to clasp 
each other, and thereby produce a regular imbricated structure ; 
the points of the lateral plates support small, short, stout spines, 
which are only seen in one of the rays of the three specimens 
before us. Where the base of the ray crosses the under surface 
of the body-dise it is firmly attached thereto, and as they ap- 
proach the centre, each of the lateral plates of the rays becomes 
greatly developed, and form by their union five channels, which 
