CARADOCIAN CYSTIDEA FROM GIRVAN. 433 



and this no doubt has strengthened his decision to place it in a separate Family. Here 

 we part company, for I regard the resemblance to the Blastoidea as purely homoplastic 

 (1900, p. 65), and have therefore retained the genus in the same Family as 

 Cheirocrinus. 



§ 280. It would be possible, while keeping all these genera in one Family, to 

 distribute them among Subfamilies ; but, since this would involve the erection of a 

 Subfamily for each genus, no practical convenience would be served by it. It will be 

 time enough to take this step when additional allied genera are discovered. 



§ 281. The following, then, is the scheme of classification to which I am led after 

 considering the theoretical opinions of Prof. Jaekel's admirable work and the new 

 genera established by Dr Schuchert (1903, 1904): — 



Fam. Echinoencrinidae : 



Echinoencrinus, Erinocystis, Glaphyrocystis, Scoliocystis, Prunocystis, 

 Schizocystis. 

 Fam. Callocystidae : 



Subfam. Lepadocystinae : 



Lepadocystis, Lepadocrinus, f Hallicystis, Tetracystis, Jaekelocystis, 

 Staurocystis, Pseudocrinus, Trimerocystis. 

 Subfam. Callocystinae : 



Callocystis, Sphaerocystis, Strohilocystis, Coelocystis. 

 Fam. Cheirocrinidae : 



Cheirocrinus, ? Homocystis, Glyptocystis, Pleurocystis, Cystohlastus. 



§ 282. Although there are reasons (§ 266) for not separating these Families from 

 other Rhombifera as a Suborder, still their close relationship must be recognised, and it 

 will save repetition in their diagnoses if they are grouped in a Superfamily. This will 

 correspond to my former Family Glyptocystidae, and I therefore designate it — 



Superfam. : Glyptocystidea. 



Diagnosis. — Ehombifera with a theca composed of five circlets of plates, theoretically 

 alternating and five in each circlet, but with two plates of Circlet I., viz. right posterior 

 and right antero-lateral, fused into one plate, 3 [for convenience the plates are numbered 

 according to the diagram, text-fig. 36], and with other plates variously modified 

 in size and position. Anus, or periproctal area, between Circlets II. and III., in 

 right posterior interradius. Hydropore in Circlet V. defines posterior interradius. 

 Pore-rhombs restricted in distribution and exaggerated in structure, forming pectini- 

 rhombs ; that uniting plates 1 and 5 is constant (exc. 2 spp. Pleurocystis). Mouth at 

 one pole of the long axis ; from it over the theca radiate food-grooves, primitively 5, 

 by reduction 4, 3, or 2 ; these are bordered by the plates of Circlet V. or by plates 

 derived from their proliferation ; and these side -plates bear facets for brachioles of 



