The Quarterly journal of the Geological Society of London . Xo. 215. 2h 482 ME. F. A. BATHER ON PETALOCRINFS. [Aug. 1898, fan as composed of three portions, L, M, and E., separated by thetwo ridges s and cZ, and each beginning with IIBr. In portion E, the branchings follow the law for the genus. Thereare ten finials, of which the two internal and the two external(using those terms througliout with reference to the whole fan) areYIBr, the others being YBr. The finials, especially the YBr, arevery long, some occupying fully three-quarters the length of thefan. The ridges are narrowest about half
The Quarterly journal of the Geological Society of London . Xo. 215. 2h 482 ME. F. A. BATHER ON PETALOCRINFS. [Aug. 1898, fan as composed of three portions, L, M, and E., separated by thetwo ridges s and cZ, and each beginning with IIBr. In portion E, the branchings follow the law for the genus. Thereare ten finials, of which the two internal and the two external(using those terms througliout with reference to the whole fan) areYIBr, the others being YBr. The finials, especially the YBr, arevery long, some occupying fully three-quarters the length of thefan. The ridges are narrowest about halfway down the arm, andthence gradually widen distalwards. Thus a single ridge narrowsfrom 4 to 2 mm., and then widens to O mm. The grooves,which are usually about o mm. wide, may be compressed to•25 mm., and widen distally to 65 mm. The ridges are alwaysnarrower than the immediately adjacent regions of the grooves thatthey separate. Pig. II. —Petalocri-nus longus. Outlineand branchinc/ ofarm-fan, x 2 diam. Pig. 12.—Hypothetical diagram of the s & d, sinistral and dextralridges; L, M, & R, left,median, and right por-tions ; I & r, left andright subdivisions of M. In portion L the branchings follow the law for the genus, exceptthat two rami of one dichotom (the internal IVBr, i. e. nextportion M) both branch at the same level. The preserved finialsare all YBr ; but since a large part is missing at the distal end, weare free to suggest that the internal branch probably, and theexternal almost certainly, forked again. In that case the finials ofportion L would precisely correspond to those of portion R. Portion M is abnormal in its branching : first, in that it does notdichotomize into divisions that are at all equal, but forks into a leftdivision with five finials (I), and a right division with two finials (r);secondly, in that the levels at which branching takes place cannot Yol. 54.] MR. F. A. BATHER OT>f PBTALOCRINUS. 433 be harmonized with the law for the genus,
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