Yol. 54.] MR. F. A. BATHER ON PEIALOORINUS. 431 



under the head of ' General Anatomy ' (p. 420). Single columnals are 

 also seen, attached to the cup in specimens a, d, & f 2, but not in g. 

 Relations to other Species. — From P. inferior this differs 

 in the smaller number of finial grooves. Prom F. visbycensis it 

 differs in the constancy of its branching ; the more restricted limits 

 of the angle of the arm-fan, which tends to be a smaller angle, 

 as explained under P. visbycensis ; the greater convexity of the 

 ventral surface ; and the less width of the ridges, as a rule. With 

 the other species comparison is unnecessary, 



P. longus, n. sp. 

 (PL XXYI, figs. 58-65 ; text-figs. 11 & 12, p. 432.). 



Angle of arm-fan, 38° ; fan divided into two unequal portions, 

 different in the number and arrangement of their grooves, by a 

 ridge to the right of the middle line in ventral aspect ; the left- 

 hand portion represents two normal halves, each smaller than the 

 right-hand portion ; finials : 10 in right-hand, 7 in middle, and 8 

 (preserved, ? 10) in left-hand portion ; ventral surface of fan almost 

 flat, bending dorsalwards slightly at proximal end ; dorsal surface 

 flat, no growth-lines or ornament seen ; ridges mostly very narrow, 

 with serrate tops. 



Type: Unique specimen in the Walker Museum, University of 

 Chicago, registered U.C. 4512. 



Locality: St. Paul, lud. (U.S.A.). 



Horizon: Niagara Limestone. 



Measurements of Specimen. — Length from ventral edge 

 of facet, 34*5 mm. Greatest width, 24 mm. Width of facet, 

 3*25 mm. Depth of facet, 1'9 mm. Thickness at distal end of arm, 

 1 mm. JS'umber of finial grooves, (26 or 27) 25 preserved. Angle of 

 arm-fan, 38°. Angle of facet, 72°. 



The branching of this arm-fan is complicated ; in discussing it, 

 the terms ' right ' and ' left ' will be used to correspond with ' right ' 

 and ' left ' of text-figs. 11 & 12 (p. 432), & PI. XXVI, fig. 60, which 

 represent the specimen in its ventral aspect. 



First, we notice that the arm-fan is divided into two portions, 

 differing in size and in the number of their branches, by a ridge {d) 

 to the right of the middle line. Further, the left and larger of 

 these two portions is again unequally divided by a ridge (s) that 

 comes nearly, but not quite, to the proximal end of the fan. A 

 normal arm-fan begins with a single and obvious bifurcation of the 

 grooves — that is, with two grooves corresponding to IIBr. Here, 

 however, it is hardly possible to distinguish the forking on either 

 side of ridges as being of a different order from the forking on either 

 side of ridge d. Theoretically it may be so : that is, the pair of 

 initial grooves on the left may represent IIIBr ; but it simplifies 

 matters to take the two portions on the left as each equivalent to 

 the single one on the right of d^ and to describe their initial grooves 

 as IIBr. The diagram (text-fig. 12) therefore represents the arm- 



Q.J. G. S. Xo. 215. 2h 



