426 MR. F. A. BATHER ON PETALOCRINTJS. [Aug, 1 898, 



that there would have been no more branching had the specimen 

 attained even greater length. 



Normal width of grooves, '9 mm. ; of ridges, 'o mm. 



Notes on the Specimen. — The law of branching is that of the 

 genus, but the median ridge does not divide the specimen into 

 similar halves, although the number of branches in each is equal. 

 This is because branchings of the same order and nature do not take 

 place at the same level, but all the branches of the right (left in 

 ventral aspect) arm- half occur from 1 to 2 mm. more proximally 

 than those of the left half. This arrangement considerably 

 diminishes the width of the arm-fan, since in no two ridges do the 

 broader regions occur at the same level. 



The ventral surface is rather less convex in both directions than 

 is that of P. visbycensis. The dorsal surface is slightly hollowed 

 along a median triangular area with proximal apex. The lines of 

 deposit of secondary stereom on the dorsal surface are well-marked, 

 and the shagreen ornament follows the lines. At the distal end are 

 depressions marking the original arm-branches ; the distal margin 

 also shows clearly the concavity of the ridges. 



The notches for covering-plates are particularly clear ; they lie, 

 not at the sides of the ridge, nor precisely on its edge, but on the 

 upper surface close to the edge ; consequently the edge itself is 

 almost straight, and the notches appear as one turns the specimen 

 from side to side. The dots of pigment along the ridges have 

 been discussed on pp. 419, 420. 



Kelations to other Species. — In dorsal aspect the angle of 

 the arm-fan might suggest comparison with P. longus ; but the 

 number and arrangement of arm-grooves is quite different. The 

 specimen cannot be considered as an undeveloped or aberrant 

 P. vishycensis : it is longer than most individuals of that species, yet 

 has no more finials than the youngest known ; on the other hand, 

 the number of finials and the narrowness of the fan are not due to 

 mere loss of certain branches, but both form part of a consistent 

 scheme of structure. These features separate the species still more 

 strongly from the others known. 



P. inferior, n. sp. 

 (PL XXVI, fig. 57 ; text-fig. 10.) 



Angle of arm-fan about 70° ; fan bilaterally symmetrical in 

 shape and, apparently, in arrangement of grooves ; finials 28 ; 

 ventral surface of fan convex ; dorsal surface not seen ; ridges 

 apparently less wide than grooves. 



Type: Unique specimen in the Walker Museum, University of 

 Chicago, registered U.C. 4736. 



Locality : Near Monticello, Jones Co., la. (U.S.A.). 



Horizon : Niagara Limestone, lower beds. 



Approximate Measurements of Specimen. — Length, 



