700 PEOF. W. J. SOLLAS ON SILUEIAN [IN'OV. 1 899, 



of any other Ophiuroid, though there is a certain amount of corre- 

 spondence in the paired structure of its five pieces. The absence 

 of any opening that could he taken for bursal apertures is note- 

 worthy. 



The position of the Eucladidae is altogether anomalous, and 

 requires at least ordinal recognition. I propose therefore to place 

 the group in a new order, the Ophiocistia, to rank as of the 

 same value as the Euryalse. The Ophiocistia are Ophiuroidea with 

 five paired series of appendages, proceeding from the ventral surface 

 of a plated test ; and in which vertebral ossicles are absent or 

 insignificant. 



Mteiastiches gigas, gen. et sp. nov.^ (^ig- 5, p. 701.) 



This remarkable form, presumably a sea-urchin, forms part of the 

 Grindrod Collection, acquired by purchase, and is labelled in different 

 handwriting ' Pish ? ' and ' Palmipes ? ' The second is a better 

 guess than the first, inasmuch as the fossil is evidently an Echino- 

 derm ; as to its class there is less certainty, but most probably its 

 affinities are with the Echinoidea. 



In the living state Myriastiches had the form of a large sac with 

 very thin walls, so that on death it suffered collapse, and now lies 

 fiattened out in a shaly limestone of Lower Ludlow age. Some 

 mud from the sea-floor seems to have penetrated to the interior, as 

 the opposite walls are separated by a thin layer of foreign material. 

 Only a part of the organism is visible on the surface of the slab in 

 which it lies ; the rest is partly concealed within the matrix, and 

 partly has been lost in extricating it. The whole of the flattened 

 sac measures approximately 10 x 15 cm. ; the part which is fully 

 exposed to view measures 8 X 12 cm. 



The ambulacral areas occupy an insignificant portion of the test, 

 which is thus almost wholly interambulacral. The 

 interambulacral areas are composed of exceedingly numerous and 

 consequently minute calcareous plates, which are almost square in 

 outline, with rounded corners ; they become hexagonal apparently 

 by truncation of opposite corners of the square. They measure 

 0*75 mm. in length and breadth, and about 0*15 mm. in thickness ; 

 the plates are closely tesselated together, though occasionally with 

 a slight degree of imbrication, the overlapping edges being adjacent 

 sides of the square, so that a lozenge-like design results. The 

 characteristic appearance resulting from the number and minuteness 

 of the interambulacral pJates no doubt suggested the reference to 

 Palmipes ; it finds no parallel among known Echinoidea. A few 

 granules, not more than two or three, occur on some of the plates, 

 but there is a remarkable absence of any indication of spines. 



The number and disposition of the ambulacral areas cannot be 

 determined. There is one which extends right across the fossil, and 

 a small fragment of another, which runs for some distance round the 

 margin. The ambulacra were probably abnormal ; if five areas had 



^ arlxo^, a row or rank. 



