436 MEMSTIC VARIATION. [part I. 



it must be a rare occurrence. In Tetracrinus the four-rayed condition 

 is normal, and it is an especially interesting circumstance that in this 

 form Variation to both a five-rayed and to a three-rayed condition has 

 been observed. For nearly all the references to the following facts I 

 am indebted to the useful collection of evidence on the subject given by 

 Bather, F. A., Quart. Jour. Geol. Soc., 1889, p. 149. 



Four-rayed varieties of five-rayed forms \ 



644. Holopus rangi. This genus was originally described from a 

 4-rayed specimen by d'Orbigny, Mag. de Zool., 1837, CI. x., PI. ill. 

 Subsequently, 5-rayed examples were obtained and this condition was 

 found to be normal (see Carpenter, Chall. Rep., xi., Pt. xxxn.,p. 197). 



645. Eugeniacrinus : departure from 5-rayed condition very rare. 

 Among many hundreds of calyces in Brit. Mus. one only is 4 rayed, 

 Bather, I. c, p. 155. 



646. E. nutans : 4-rayed specimen at Tubingen figured in Quenstedt's 

 Atlas to Petrefactenk. Deutschl. Taf. cv., figs. 179 — 181. Another case 

 Goldfuss, Petreficta Germanic, i., p. 163, PI. I., fig. 4, now in Poppels- 

 dorf Mus., Bour. (Bather). 



647. E. caryophyllatus : 4-rayed specimen seen at Stuttgart. Such 

 a specimen [] the same] Rosinus, Tentaminis de Lithozois...Prodr. &c, 

 tab. in. (Hamb. 1719). Another case Goldfuss, I.e., fig. 4: now in 

 Poppelsdorf Mus. (Bather). 



648. Pentacrinus : a 4-rayed stem-joint from the Chalk, Mantell, G. 

 A., Geol. of Sussex, 1822, p. 183 : now in Brit. Mus., E. 5501 (Bather). 



649. Pentacrinus jurensis : 4-rayed specimen. The stalk had only 

 4 sides, one being quite flat. This flat side had an articulation for a 

 cirrus, de Loriol, P., Paleont. Franc, Terr, jur., Ser. 1, Paris, 1886, 

 p. 112, PL cxhiv.,fig. 6. 



650. P- subsulcatus : 6 joints of a 4-rayed stem, ibid., p. 117, PI. 

 cxlv., fig. 2. 



651. P- dumortieri : 8 joints of a 4-rayed stem, ibid., 1887, p. 186, 

 PI. clxii., figs. 6 and 6 a. 



652 P- dubius : 4-sided stem quite regular. Basle Mus., Bather, I.e., 



p. 168. 



653. Balanocrinus subteres : 4-sided stem quite regular, ibid. 



654. B. bronni : " the articular surface shows 4 sectors quite regularly 

 disposed ; this peculiar character is continued over the whole series of 

 joints, 26 in number." ibid. 



655. Encrinus fossilis : a 4-rayed calyx, &c, v. Strombeck, A., 

 Ztschr. d. deut. geol. Ges., I., 1849, p. 158 et seqq. See also Palaionto- 

 graphica, 1855, iv., p. 169, PI. xxxi. figs. 1 and 2. 



656. E. fossilis : two 4-rayed calyces with mutilated arms, v. Koenen, 

 Abh. k. Ges. d. Wiss., Gbttingen, 1887, xxxiv. Phys. Kl., p. 23. 



657. Antedon rosacea : 4-rayed specimen, Carpenter, P. H., Chall. 

 Rep., xxvi. Pt. lx. p. 27. Four-rayed Japanese specimen, ibid. 

 Another in Brit. Mus. ibid. 



1 4-sided stem joints undetermined. Pdsch, Poleiis PaUiont., 1837, p. 8, PI. u. 

 fig. 8, a, b, c, d. See also Austin, Ann. and Mag. N. H., 1843, xi. p. 203. 



