﻿SCHUCHERTj SILURIC AND DEVONIC CYSTIDEA 2 23 



I'.asal row has plates 4, 1, 2, 3. 



Second row has plates 5, 6, 7, 8, 9. 



Third row lias plates 10, II, 12 (7, 8), 14. 



Fourth mw has plates [6, 17, [8, 13 (19 absent), 15. 



Fifth row has deltoid 23. 



Deltoid 23 is a very small plate situated at the top of plate 18 and 

 between it and plate 13. It has a comparatively large hydropore, 

 but a madreporite does not seem to be present. Plate [9 of other 

 genera is nol developed in this genus. Anal area small hut conspicu- 

 ous and protruding, consisting only of the pyramid of 6 pieces. The 

 prominence of the anal area is dm- to the protrusion of the bounding 

 thecal plates of which there are 4, i. e., 7. 8, 13, .and 14. ( )ne basal 

 and 2 upper very small discrete-pectinirhombs. The parts on plates 1, 



12, and 14, as a ride, do not show the dichopores, since these are 

 deeply situated each in a pit with a high margin. Dichopores few. 



Ambulacra normally 4 in number. These are R I, R V, R IV, 

 and R II. In rare cases, either R I or R II may be absent, or R V 

 may be forked. Ambulacra depressed, more or less deeply ex- 

 cavated, and, in normal individuals, continuing to or near to the 

 column. Brachioles moderately abundant, short and stout. 



Column comparatively stout. Length unknown. 



Genotype, /. hartleyi Sehuchert. 



Jaekelocystis seems to have closest relationship with Apiocystites 

 and therefore, also, with Lepocrinites. It is readily distinguished 

 from these genera in that it has but 18 thecal plates, plate 19 not 

 being developed. The same difference is found when Jaekelocystis 

 is compared with Staurocystis. Even should plate 19 be present as a 

 very minute piece, this genus would still differ from Apiocystites and 

 Lepocrinites in that its third row of thecal plates has but 4, while in 

 the latter genera it has 5, plates. In other words, in these two genera 

 plate 13 is in the third row, while in Jaekelocystis it is in the fourth. 

 Another difference distinguishing this genus from all other asso- 

 ciated cvstids with 4 simple ambulacra lies in the composition of the 

 anal area, which consists only of the pyramid of 6 pieces. In the 

 other genera there is always an additional circle of small pieces. 

 Moreover, in Apiocystites and Lepocrinites this area is bounded by 

 plates 7, 8, and 13, while in Jaekelocystis there are 4 plates — 7, 8, 



13, and 14. 



Tetracystis also has 4 ambulacra and but 4 plates in the third 

 circle of the theca. However, it differs from Jaekelocystis in having 

 plate 19, and therefore has 6 plates in the fourth circle of the theca. 

 Further, the anal area has a circle of plates .around the pyramid, the 



