﻿schuchert] siluric and devonic cystidea 247 



Definition. — Callocystinse ? having a depressed globular theca with 

 a deeply invaginated base, and normally composed of 24 plates ar- 

 ranged as follows : 



Basal row has plates 4, 1, 2, 3. 



Second row has plates 10, 5, 6, 12. 7, S, 14. <>. 

 Third row has plates 16, 11, 17. 18, 13, [9, 15. 

 Fourth row has deltoids 20, 21, 22, 23 double, and 24. 



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Fig. 36. — Analysis of Ccelocystis sitbglobosus (Hall). 



Anal area bounded by plates 7, 8, and 13. The anal pyramid is 

 apparently not surrounded by a circle of small plates as in Sphcero- 

 cystites. 



Pectinirhombs normally situated, small, discrete, and with but few 

 dichopores. 



As all the specimens are internal casts of the theca, the nature of 

 the ambulacra, anal area, sculpture, and the column cannot be stated. 



Genotype, Hemicosmites sitbglobosus Hall. 



The foregoing definition and the diagrams here given show that 

 Ccelocystis differs widely from Splucrocystitcs in that it has 6 addi- 

 tional plates and these have a quite different arrangement. The 

 second row of the former genus has all the plates of the latter and in 

 addition plates 10, 12, and 14; the third row has 7 plates and in- 

 cludes all the plates of the fourth row in Sphcerocystites, while the 

 deltoids of the fourth row in Ccelocystis, 5 in number, are not present 

 (except 23 which is not double) in Splucrocystitcs. 



A comparison of this diagram with that of Sphcerocystites Taekel 

 (not Hall), in the work cited, shows that that author omitted plate 

 10 in the second row. Jaekel's diagram therefore has 24 plates, 

 while that here represented has 25, counting the parts of plate 23 as 

 separate pieces. The writer's material is excellent, and while con- 

 siderable variation in the shape of the plates exists in different speci- 

 mens, there seems to be little chance for error in the interpretation 

 of their arrangement as given in text-figure 36. 



