A MONOGRAPH OF THE EXISTING CRINOIDS 61 



(1) Tribe Comasterida (Comasteridae only). 



(2) Tribe Mariametrida (Zygometridae, Himerometridae, Mariametridae, 



Stephanometridae, Tropiometridae, and Colobometridae). 



(3) Tribe Thalassometrida : 



(a) Subtribe Thalassometrida (Thalassometridae, Charitonietridae, and 



Calometridae). 

 {b) Subtribe Notocrinida — 



1 . Section including the Notocrinidae. 



2. Section including the Asterometridae, new family {Asterometra 



and Pterometra) . 



(4) Tribe Macrophreata: 



(a) Group including forms with the centrodorsal more or less hemispherical, 

 rarely discoidal, and its internal cavity rather moderate; cirri arranged 

 in alternating rows (Antedoninac, Perometrinae, and perhaps also 

 Thaumatocrinus) . 

 (6) Group including forms with the centrodorsal conical to coliunnar and 

 its internal ca^'ity excessively large; cirri in columns, or tending toward 

 columns (Zenometrinae, Bathymetrinae, Heliometrinae, fComatonia, 

 Isometrinae, Atelecrinidae, and Pentametrocrinidae [perhaps excluding 

 Thaumatocrinus] ) . 

 Doctor Gisl^n suggested that the subfamOy Perometrinae was possibly developed 

 from the Colobometridae in the direction of the Macrophreata. He also remarked 

 that Comatonia differs from all other comasterids in having a rounded-conical centro- 

 dorsal with the cutI in 3 or 4 rows and strong synarthrial processes, as well as in the 

 possession of sacculi. He gave it as his opinion that Comatonia is a macrophreate 

 form possibly related to the Heliometrinae. 



Gisl^n's discussion of the groups of recent comatulids established by him is as 

 follows : 



(1) Comasterida. Centrodorsal discoidal. Centrodorsal cavity (excepting in 

 small forms, as for instance Comatilia) small and shallow. Cirri often rudimentary 

 or lacking, rarely more than a double row, the rows almost always alternating (the 

 exception being Palaeocomatella). Cirrus sockets without sculpture. Basal star 

 sometimes developed. Articular faces of the radials vertical. Radial cavity large, 

 filled by a large central calcareous plug. Muscular fossae on the articular faces of 

 the radials very low broad bands. Arms 10 or more. Number of the elements in the 

 division series in the multibrachiate forms often very variable in closely related 

 groups, as well as in different rays of the same individual. Synarthries weakly 

 developed, often replaced by cryptosynarthries, pseudosyzygies, or syzygies. No 

 synarthrial tubercle or synarthrial backward projection. Many syzygial septa 

 (except in small forms). Syzygies usually numerous. Covering plates in Nemaster 

 and Comatilia. Pear-shaped organs instead of sacculi. The proximal and some- 

 times the distal pinnules also with a comb (combs elsewhere occurring, in rudimentary 

 form, only in the Heliometrinae). Pi the longest proximal pinnule, the succeeding 

 pinnules decreasing in length regularly. Distal pinnules with strong hooks on the 

 most distal segments. Disk often exocyclic, sometimes with calcareous granules. 



