MITRASTER. 57 
line are much larger and higher than the other plates. The plate adjacent to the 
median interradial line measures about 4mm. in length and 4 mm. in height; 
the next plate 5 mm. in length, and from 3°5 mm. to 3°75 mm. in height. The 
surface of the plates is marked with small widely spaced punctations, and there is 
a narrow depressed border round the entire margin of the plate, which is very 
finely punctate. 
The actinal area is unknown to me. 
History.—The fossil delineated on Pl. XIV, fig. 5a, was drawn by Mr. A. H. 
Searle under Dr. Wright’s instructions, but I regret that I have not been able to 
find any trace of the specimen. I am therefore led to believe that the type 
belonged to Dr. Wright’s private collection, which has been distributed since his 
lamented death. Knowing by experience the extreme care and fidelity which 
characterise all Mr. Searle's work, I have ventured to describe the species from 
his drawings alone, for it seemed undesirable to leave such an interesting form 
without notice; and I am hopeful that the publication of the figure and the 
description of its characteristic features will lead to the detection of the type. I 
am unable to give any information as to the locality or stratigraphical position 
from which the fossil was obtained. 
Remarks.—The rather small size of this example and the small number of 
supero-marginal plates—only four for the whole side of the disk—would not 
unnaturally suggest at first sight that this was possibly animmature form. After 
careful study, however, I do not consider such to be the case, or at any rate I am 
unable to regard the fossil under notice as the young of any of the species with 
which I am acquainted. The large and characteristically developed ultimate 
supero-marginal plates in conjunction with the presence of a normal number of 
infero-marginal plates, together with the fact that the size of the test is not less 
than that of another perfectly characterised species, lead me to rank this as a 
distinct species with little hesitation. The general proportions as well as the 
character of the different plates, and the facies of the form as a whole, appear to 
me to fully warrant this view. 
Genus—MITRASTER, Sladen. 
(Mirpa = a broad belt, or girdle.) 
Body depressed and cycloid, or cyclo-pentagonoid in contour. Marginal plates 
with co-ordinated granulose elevations and punctations, and a surrounding narrow 
