REPORT ON THE CRINOIDEA. 27 



E. Some Abnormal Conditions of the Bays of Comatul^. 



In the two large genera Antcdon and Actinometra, just as in Apiocrinus, Pentacrinus, 

 and Encrinus, there are normally five rays which divide upon the third joint above the 

 basals, i.e., the third radial is the axillary (Pis. VIII., LXVII.) ; and this is the general 

 rule among the Neocrinoids. The exceptions are Metacrinus and Plicatocrinus, the 

 former with four or six radials (primitively five or eight, as some of them are syzygial 

 joints), and the latter with only two as in one or two fossil Comatulse. It sometimes 

 happens, however, that an additional radial is inserted into the normally three-jointed 

 series, as for example in the Pentacrinus millleri mentioned in Part I., 1 and I have met 

 with a nearly similar case in Antedon alternate/, (PL XXXII. fig. 5); while Wagner 2 has 

 noticed the same monstrosity in Encrinus gracilis. But the two outer radials of Antedon 

 alternata remain separate and are not united by syzygy, as in the Pentacrinus millleri 

 just mentioned. On the other hand, in one example of Antedon remota (PI. XXIX. 

 fig. 6) and in the only specimen of Antedon incerta (PI. XVIII. fig. 4) and in one of 

 Actinometra parvicirra (PI. LXI. fig. 1) the second radial is missing in one ray and 

 the axillary rests directly against the first radial as in Plicatocrinus and in many Palseo- 

 crinoids. 



Another and more common variation is in the number of the rays themselves. 

 Excepting, of course, in Promachocrinus there are normally five rays in all Comatulidae ; 

 but forms with four and six rays are occasionally met with. I have a tetraradiate 

 specimen of Antedon rosacea, and one of a Japanese Antedon in Dr. Doderlein's 

 collection, and also one of Actinometra paucicirra from Cape York. In all these three 

 individuals the anterior ray (A) is missing, so that the mouth, instead of being radial 

 in position, is placed interradially between the rays E and B. 



On the other hand the " Blake" collection contains a six-rayed form of Actinometra 

 pulchella. The disc is unfortunately concealed, so that the symmetry of the ambulacra 

 cannot be made out. But I am rather inclined to think from the appearance of the 

 centro-dorsal that it has the usual pentamerous symmetry, one of the radials being rather 

 larger than its fellows and also axillary, so that it bears two small rays, as sometimes 

 happens in Allagecrinus. 3 Another variation characteristic of this genus occurs in 

 Actinometra midtibrachiata (PL LVI. fig. 3), one of the radials being considerably smaller 

 than the other four. 



The only other six-rayed Comatula that I know is a small and dry Antedon in the 



1 Zool. Chall. Exp., part xxxii. p. 311, pi. xv. fig. 2. 



2 Die Encriniten des unteren Wellenkalkes von Jena, Jenaische Zdtschr., 1886, Bd. xx. (N.F. xiii.), p. 20, Taf. ii. 

 fig. 13. 



3 See Carpenter and Etheridge, Contributions to the Study of the British Paleozoic Crinoids, — No. I. On Allagecrinus, 

 the Representative of a New Family from the Carboniferous Limestone Series of Scotland, Ann. and Mag. Nat. Hint., 

 1881, ser. 5, vol. vii. pp. 288, 292. 



