236 CATALOGUE OF THE BLASTOIDEA. 



concave below, flattened upwards towards the summit, which is rounded, and some- 

 times contracted ; periphery at or near the margin of the flattened base ; section 

 distinctly pentagonal, with the angles at the periphery occupied by the radial lips. 

 Basal plates sunken, not visible, placed within the basal concavity or depression. 

 Radial plates very long, narrowed towards the base, and occupying two planes — one 

 part is horizontal, and assists in forming the base, while the other is more or less at 

 right angles to it, and constitutes the limbs; radial sinus very long and narrow, 

 more than two thirds the length of the entire plate ; lips obtuse. Deltoid plates 

 relatively small, and unequally rhombic ; the anal deltoid flatter than the others. 

 Ambulacra long and much curved, widest at the level of the radio-deltoid sutures, and 

 gradually narrowing to the prominent apices ; lancet-plates completely concealed by the 

 side plates, which are large, very numerous, wider than the lancet-plates, and bent down 

 at a considerable angle on each side of the ambulacra ; pores large and very numerous, 

 one hundred and more on each side. Spiracles ovate-oblong, their distal ends resting 

 on the radio-deltoid sutures. Mouth small. Anus oblong and close to the peristome. 

 Column large ; columnar facet within a deep basal concavity. Ornament not preserved. 



Remarks. The specimen described above is one of the largest of our British 

 Blastoids, measuring 30 mm. in height by 25 mm. across the base. We think that 

 there can be little doubt of its identity with the Mitra elliptica of Cumberland, 

 although it differs from his figures in one or two points. He represents the central 

 half of the flattened base of the calyx as occupied by five basal plates, a number 

 which occurs in no known Blastoid ; and we cannot help suspecting that this must 

 be erroneous. In our specimen the centre of the base is occupied by a circular 

 concavity, which is filled with calc-spar, the remains of the upper stem-joints 

 (PI. XIII. fig. 17). The interradial sutures extend downwards as far as this hollow, 

 which probably contains the basals just as in Elceacrinus (PL II. fig. 45) and in 

 Granatocrinus ellipticus (PI. VIII. fig. 18). But it is relatively smaller than the 

 pentapartite base of Cumberland's figure. Then, again, Cumberland spoke of and 

 represented the interradial sutures as extending right up to the peristome, while 

 there is no trace of spiracles in either of his figures. But as some of his other 

 figures are equally incorrect, e. g. those of Mesohlastus elongatus ( = Mitra elongata, 

 Cumb.), we do not attach very much importance to this point. 



There is one character of Acentrotremites ellvpticus about which we are somewhat 

 uncertain. We refer to the existence of an hydrospire-plate. The condition of the 

 ambulacrum figured on PL XIII. fig. 19, seems to indicate its presence; but we are 

 by no means satisfied about it, and must leave this point to be worked out when 

 better material is available. 



Cumberland gives no locality for his specimen, but described it as consisting of 

 white limestone like Mitra elongata, which occurs in Lancashire and Yorkshire, and 

 w£ conclude, therefore, that his specimen of M. elliptica, which seems to liave 



