John Rofe — Notes on the Crinoidea. 267 



third, and in some repects a rather more perfect specimen, from 

 Clithero, is now in my hands, and from it, with the help of those in 

 the Museum, the genus may be, in some respects, more fully de- 

 scribed. Using M. de Koninck's nomenclature of the plates, it may 

 be represented as having a base pentagonal and tripartite, small and 

 pierced for a pentaphylloid central canal ; subradials, four pentagonal, 

 about as wide as high, one hexagonal, one and a half times as high 

 as wide, which is the first anal plate. The base-lines of two of the 

 pentagonal and of the hexagonal plate are not quite straight, but fit 

 into the very obtuse angle formed by the junction of the plates of the 

 base. There are five sets of primary radial plates, the third plate 

 bifurcating, or sometimes the fourth, even in the same specimen, an 

 irregularity which I have observed occasionally in the Actinocriniis. 

 All the radials are about twice as wide as high, and are thick, and 

 overlap on the lower side, falling over and hiding a recess in the 

 plate under it, making the second and third radials appear to be 

 concentrically curved both top and bottom, but at the back of the 

 plates the joints are straight, as shown on the face as in Figs. 11, 

 11a, and 11& is a section of two plates showing the overlap. The 

 joints are wrinkled on the face and at the angles rather more coarsely 

 than is the case with many other Crinoids. This overlap must add 

 to the strength of the unusually wide cup, and, so far as my experi- 

 ence goes, it is peculiar to this genus. Of the inter-radial plates one 

 series consists of a single row standing on the anal plate; the others^ 

 are irregular, but generally similar in arrangement to those of the 

 Actinocrinus. 



EXPLANATION OF PLATE XI. 



Fig. 1. — Cross section and side view (Fig. la.) of a column and side arm, showing the 

 branching of the central canal of the side-arm from that of the column, 

 and on the side view showing the obtusely conical seat of a side-arm. 



Fig. lb. — Conical end of a side-arm detached from its seat. 



Fig. Ic. — Cross section of a column, through two side-arms, showing the connexions 

 with the central canal. 



Fig. 2. — Side view of a column and side-arms, showing the gradual expansion of the 

 plates of the column to suit the growth of the side-arm. 



Fig. S. — Portion of a section of a column, vdth bifurcation of the strise. The central 

 portion decomposed. 



Fig. 4. — Portion of a large weathered column showing concentric rings of increase. 



Fig. 5. — Section of Rhodocrmus, the lower part of the interior filled with consoli- 

 dated sand. 



Fig. 6. — Section of a column partially filled with consolidated sand, the remainder of 

 the interior being subsequently filled with Calc-spar. 



Fig. 7. — Section of a column of a Liassic Pentacrinite. 



Fig. 8. — Section of an elliptical column of Mountain Limestone Tlatxjcriniis, 



Fig. 9. — Section of a column of Apiocriniis (Oolitic), showing structure and rings of 

 increase. 



Fig. 10. — Section of a subpentagonal column from Mountain Limestone. 



Fig. 11. — Side view of part of the calyx of Euryccrinus, showing arrangement of 

 radial and inter-radial plates. 



Fig. 11a, lib. — Face and section of two radial plates of Euryocrinus, showing the 

 overlapping of the plates. 



