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SILURK WD DEVONIC CYS1 [DJ \ 



239 



Iacra in Pseudocrinites should represent R I and R \\ . Moreover, 

 the madreporite, hydropore, and pectinirhombs 1 and 5, and 12 and 

 18, in Trimerocystis will then lie between R I and R IV. and pectini- 

 rhombs i-( and [5 between R V and R IV. The three following dia- 

 grams will make this correlation more clear: 



IV" 



IV 



Fig. 33. — Diagram showing relation of ambulacra in (a) Tetracystis, (b) 

 Trimerocystis, and (c) Pseudocrinites. 



For these reasons the writer has changed the nomenclature of the 

 rays in Pseudocrinites from R II and R V to R I and R IV. 



Though Trimerocystis is based on a single specimen, having 

 obvious relations to Pseudocrinites elarki, it cannot be regarded as a 

 monstrosity of that species, because the two forms do not occur in the 

 same bed. Trimerocystis peculiaris was not found in the cystid 

 horizon at Keyser, but above it (probably less than 10 feet), in asso- 

 ciation with Caiuarocriiius, and is the only known cystid in this zone. 

 Under these circumstances, and in order that the generic definition 

 of Pseudocrinites may stand, the writer has deemed it advisable to 

 erect a new genus for this 3-rayed type. 



TRIMEROCYSTIS PECULIARIS n. sp. 

 (Plate XXXV, figures 1-3) 



Length of theca 35 mm. ; width 26 mm. ; depth 20 mm. Base of 

 theca deeply excavated and occupied by a stout column. For general 

 form, shape of individual plates and their ornamentation, see figures 

 1-3, plate xxxv, and text-figure 34. 



Ambulacra prominent, rounded, extending along three sides, bent 

 around the excavated base of the theca, and touching the column. 

 Each ambulacrum has on one side about 30 brachioles, or 60 to each 

 ray, and about 180 on the entire theca. Brachioles apparently not 

 very stout nor long, and composed of rather large pieces. Ambu- 

 lacral grooves narrow, but deep, and covered by a series of small 

 ambulacralia arranged much as in Pseudocrinites perdewi, with the 

 pieces somewhat larger. 



