434 ME. F. A. BATHEE ON PETALOCRINUS. [Aug. 1 898, 



size and abnormal construction, it is exactly the opposite of P. an- 

 gustus in its mode of branching. Whereas in the latter species the 

 branching is accommodated to the narrowness of the fan, in 

 P. longus it is as unaccommodating as can be, and the numerous 

 branches are squeezed into the constricted space by the narrowing 

 of both grooves and ridges. In its tripartite division and the 

 resultant greater number of its branches, P. longus is the analogue 

 of P. expansus ; but whereas in that species the fan is increased 

 in widtb, not merely by the number of grooves but by the breadth 

 of the intervening ridges, in P. longus the width of fan, grooves, 

 and ridges is diminished. As regards the other species, even if we 

 disregard the abnormality and the angle of the fan, there remain 

 as clear differences the mode and number of branchings, the narrow-' 

 ness of grooves and ridges, and the length of the fan. 



P. expansus, n. sp. 

 (PI. XXV, figs. 33-36 ; text-figs. 13 & 14, p. 435.) 



Angle of arm-fan, 90° ; fan divisible into three portions, each 

 corresponding to half a normal arm-fan ; finials in each third 9-10, 

 total preserved 28 ; ventral surface of fan flat, bending dorsalwards 

 very slightlj^ at proximal end ; dorsal surface not seen, no trace of 

 ornament on portions visible ; ridges much wider than grooves, and 

 flat-topped. 



Type: Unique specimen in Hiksmuseum, Stockholm. 



Locality: Wisby (Gotland). 



Horizon : Upper Silurian, base of bed f of Lindstrbm. 



Measurements of Specimen. — Length along ridge tZ, 

 21*25 mm. ; length along ridge 5, 18-9 mm. ; greatest length, which 

 is immediately right oicL 24 mm. ; greatest length of portion left of 

 s, 20'5 mm. ; width of specimen, as preserved, 22-5 mm. ; width of 

 specimen, as restored, 28*5 mm. ; width of portion left of 5, as 

 restored, 10 mm. ; width of portion right of s, as restored, 18*5 mm. ; 

 width of facet, 3*5 mm. ; depth of facet, 1*9 mm. ; normal width 

 of groove, -8 mm.; greatest and least width of ridge c?, 1*5 and 

 •5 mm. ; greatest and least width of ridge s, 1*9 and '9 mm. 



The branching of this arm-fan is comparable with that in the 

 type-specimen of P. longus, and may be described in a similar 

 manner by dividing the ventral surface into portions L, M, and E,, 

 separated by ridges s and d (text-fig. 14). 



A ditference is at once seen in the closer connexion of L and M, 

 since the initial groove of L obviously arises from the IIBr groove 

 of M. So long as this fact is duly recognized, it will facilitate 

 description to regard the initial groove of each portion as IIBr, as 

 was done in P. longus. 



The 9 finials of L may thus be termed, reading from left to right : 

 VI, VI, V, V, V, V, V, V, V. Similarly the 9 finials of M are ; 



V, V, V, V, V*, V, V, VI, VI ; while the 10 finials of E are : 



VI, VI, V, V, VI*, VI*, V, V, \, V. In each portion the branching 



* VI*, VI '^ are produced by the forking of the branch corresponding to V*. 



