OPIIIURELLA. 155 
Forest Marble, near Wollaston, I find the lateral plates pass round and apparently grasp 
the sides of the arms in a very distinct hook-like fashion. From the free border of these 
lateral plates several short thorn-like spines project obliquely outwards ; between the central 
and lateral plates two rows of apertures are formed by the mode these elements of the 
rays are articulated together ; the arms are round, from three to four times the 
length of the diameter of the body, and taper very gently from the disk to their termina- 
tion. Since my plates were drawn I have seen a slab, collected from the Forest 
Marble, near Weymouth, by my late friend the Uev, S. Cooke, F.G.S., on which two 
specimens of this species are exposed lying on their under side and exposing the upper 
surface of the disk and arms. The disk is composed of ten radial-plates, united in pairs, 
and forming five heart-shaped shields, which cover the arms ; between them the disk is 
depressed and undulated at the circumference. On its upper surface several thin small 
scales are arranged in an imbricated manner and form a radiate pattern towards the centre. 
The upper plates of the arms consist of two halves united by suture in the middle line ; 
with the lateral plates they curve obliquely outwards clasping round the rays, and 
terminate beneath the ventral plate, as shown in fig. 3 h and fig, 4. 
fig. 3 a the under surface of the disk and arms of this species is shown of the 
natural size. Fig. 3 (5 is the same specimen, magnified three and a half diameters, an din 
fig. 4 I have shown a portion of one of the arms with the spines articulated to the free 
margin of the plates, and magnified six diameters. 
Affinities and Differences. — This Brittle-star resembles OpJdolejiis Murravii. It is 
altogether a more slender form, Mdth a proportionately wider disk having larger and more 
awl-shaped arms. In the structure of the ray-plates there is likewise a very important 
difference, 0. Murravii having the encircling plates on the lateral parts of the rays, with 
a total absence of the chain-like structure which distinguishes 0. GriesbacJdi. 
Locality/ and Stratip-aphical Position. — This Ophiurella was first discovered by the 
late Rev. W. Griesbach in the beds of Forest Marble, near Wollaston, who generously 
supplied me with several good specimens, one of which I have figured with details. 
I have a fair specimen from the Great Oolite of the Windrush Quarries, near 
Sherborne, Gloucestershire, in a rock similar to that which yielded Solaster Moretoni, 
Forb., so that both these extinct Sea-stars lived together in the same ocean. 
My late friend, Rev. S. Cooke, F.G.S., collected several thin slabs of Forest Marble, 
near Weymouth, on which many beautiful specimens of this species lie in bold relief, 
and these specimens have enabled me to make out the structure of the upper surface of 
the disk and rays : all the other specimens which I had previously examined displayed 
only the ventral aspect of this Ophiurella ; which appears to be limited to the upper 
portion of the Lower Oolitic Formation, as no evidence of its existence has been 
found in the MurchisoncB, Soioerhyi, and Parlcinsoni zones, which faithfully represent the 
three divisions of the Inferior Oolite in the English, French, and German Jurassic 
strata. 
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