﻿schuchert] siluric and devonic cystidea 241 



normally situated, with long- angulated rhombs and numerous single 

 pores." 



His remarks are as follows: 'The theca on account of the 4 

 ambulacra is 8-sided in transverse section; the free sides arc slightly 

 domed and in the middle are nearl} twice as wide as the ambulacra. 

 Plate 14 abuts but very little against the anal area. The 4 ambu- 

 lacra are the same as those of the Apiocystids, namely R I. lv 11. 

 K [V, R V. They are equally developed and without exception con- 

 tinue to the base of the column. The number of brachioles is about 

 40 to each ambulacrum. The anus and the pectinirhombs, built and 

 situated as in Psendocrinites, arc equally divided on the thecal sides 

 between the ambulacra, so that the anus lies between R IV and R V, 

 the basal rhomb between R 1 and R II, and the upper rhombs, one in 

 each of the other two areas." For reasons mentioned in discussing 

 Trimerocystis, the present writer regards the anus as between R I 

 and R V. 



The description and figures show clearly that Staurocystis is very 

 closely related to Pseudocrinites, the plate structure being precisely 

 the same in both; this is also true of the structural detail in the 

 ambulacra. The former genus differs from the latter only in being 

 8-sided (essentially 4-sided) and in having 4 full-length ambulacra, 

 Pseudocrinites being 2-sided and having but 2 ambulacra. Though 

 Trimerocystis, also, is closely related, it differs from the other two. not 

 only in being 6-sided (essentially 3-sided) and in having 3 ambulacra, 

 but also in the arrangement of the thecal plates. These 3 genera 

 agree in this, that the anal area consists of 2 circles of pieces and is 

 placed between plates 7, 8, 13, and 14. Pseudocrinites and Stau- 

 rocystis further agree in having the plates of the theca arranged alike, 

 but in Trimerocystis they are disposed differently. This difference 

 may best be expressed in tabular form, thus : 



Basal Circle 



Circle 2 Circle 3 Circle 4 



Pseudocrinites 

 Staurocystis 

 Trimei 1 



4-1-2-3 5-6-7-S-9 10-11-12-14 1 6-1 7- 1 8- 13- 1 9-1 5 



4-1-2-3 5-6-7-8-9 10-11-12-14 16-17-18-13-19-15 



4-1-2-3 j 10-5-6-7-8-9 ; 16-11-12-14 17-18-13-19-15 



Forties's figure 7 shows the anal area surrounded by plates 7, 8, 13, 

 19, and 14, but in bis description he adds that " there is not sufficient 

 material to make out the arrangement of the plates completely " (p. 

 499). Jaekel's diagram of this region, however, shows that plate 19 

 of Forbes is a part of plate 13, and that the arrangement of the thecal 

 plates around the anal area is as stated above, i. e., 7, 8, 13, and 14. 



