408 MB. r. A. BATHER 01*r PETALOCRINFS. [Aug. 1 898, 



readily studied in P. visbyce'osis, and the description will be based 

 chiefly on that species. 



The Dorsal Cup is bowl-shaped; flattened dors ally, with slightly 

 concave base ; sabpentagonal in outline, owing to the lateral posi- 

 tion of the radial facets, and very slightly excavate in the interradii ; 

 low, the height being about half the width. The measurements of 

 five specimens are given in the table on p. 430. 



The cup was described by Mr. Weller as composed of radials and 

 basals only, i. e. as that of a typical Monocyclic Inadunate crinoid, 

 and he compared it to the cup of Platycrinus. This is in fact the 

 appearance presented by d and f2; but in those specimens the 

 sutures are very obscure. In g, to judge from the photographs 

 and plaster cast, the plates are clearly separate, and the basals 

 appear not to come right up to the abactinal centre, but to leave a 

 concavity a little larger than the space occupied by the proximal 

 column al, which does not seem to be present in the specimen (text- 

 fig. 1, p. 401). This appearance is pronounced in specimen a, and here 

 the interbasal sutures are distinctly seen to stop before reaching 

 the column al, while in the interradii arbitrarily designated iii-iv, 

 iv-v in PI. XXVI, fig. 42, obvious sutures are seen dividing the 

 basals from the depressed area round the stem-attachment ; in this 

 area itself an interradial suture can be distinguished clearly in 

 interradius iv-v, less clearly in interradius iii-iv. Although the 

 surface is corrugated b}^ the petrifying processes above described, 

 there is no room for doubt as to the correctness of this description ; 

 and it was independently confirmed by two unprejudiced observers, 

 Mr. H. W. Burrows and Mr. G. P. Harris, whose accuracy is well 

 known to palaeontologists. The important conclusion follows that 

 the base is dicyclic, there being a circlet of infrabasals, minute 

 but distinct, largely covered by the proximal columnal, and perhaps 

 partly fused, but not into a single plate. 



Basals (BB) 5 ; pentagonal, slightly wider than high, subequal. 

 Owing to the absence of anals from the cup it cannot be seen 

 whether there is any differentiation of a posterior side ; in a the 

 basal in interradius ii-iii is perhaps the largest, those in iv-v and v-i 

 being smaller than the rest. The proximal portions of the basals 

 are included in the central concavity. 



Radials (BE,) 5, subequal ; height to base of facet about | width. 

 They are of the shield-shape usual in Inadunate crinoids ; their 

 proximal portions enter the flattened dorsal area ; thence the plates 

 curve upwards to the facet, but the curve is more pronounced in 

 the interradii, so that the radials project towards the facet, the plane 

 of which is almost parallel to the vertical axis of the cup, but a 

 little sloping outwards ventro-dorsally. Taking the width of the 

 radial as 100, the average width of the facet is relatively : — in f I, 

 o5-5 ; in a, 80 ; in d, 65*2 ; in g, 77. The specimens are here 

 arranged in order of size, and it is seen that this considerable varia- 

 tion can scarcely be due to difference in age. There is also variation 

 between the facets of an individual, though less in amount, as seen 

 from the table of measurements on p. 429. The articular surface 



