444 DR F. A. BATHER. 



um bones on the plates of Circlets II. and III. (PL IV. fig. 56). In Circlet IF. the 

 umbones are below the centres of the plates. In Circlet III. they lie about half-way 

 up the plates, but are shifted to the right or left of the median vertical line according 

 to the modification of the plate ; only in plate 1 1 can the umbo be considered approxi- 

 mately central. In Circlet IV. the ridges ascending from Circlet III. meet at a point 

 a little below the lip of the subvective area. 



§ 317. The surface of the plates is ornamented with a very fine granulation. This 

 is crossed by almost imperceptible growth-lines or faint folds parallel with the sutures, 

 and between these folds the granules tend to fuse into short irregular linear series 

 radiating from the umbones. This is best shown in Gl57 and G137, also in an isolated 

 plate, Gl80, in which the stereom is preserved (PI. IV. fig. 56); but even in these 

 the attempt at description seems to indicate greater definiteness than really exists. It 

 is far finer and fainter than the ornament described by Jaekel as " Gitterstruktur," and 

 explained by him as the crossing of growth-lines by subsidiary axial ridges. 



§ 318. As usual in the genus the plates are very thin : "15 mm. at the edge of the 

 completely preserved plate Gl80. 



§ 319, The Pectinirhombs are all complete and conjunct, and are confined to the 

 following sutures : 1-5, 10-14, 13-18, 15-16, 16-17, 17-18, 18-19, making a total of 

 seven. The demirhombs 1-4 and 1-2 usual in this genus, and the complete rhomb 

 1-6 found in all other species of the genus, are certainly absent. Of the rhombs con- 

 necting the plates of Circlet IV. only one is absent, and that one, 15-19, is just the one 

 that might be expected to disappear on the hypothesis that the distribution of the 

 rhombs is controlled by the course of the gut. The rhombs of the lower circlets are 

 reduced to three, and it is worth noting that these are not the same three as in either 

 Echinoencrinidae or Pleurocystis. 



§ 320. The rhombs are surrounded by no raised margin. The number of folds is 

 approximately as follows: in 1-6, ? 30 (Gl65); in 10-14 from 32 (Gl66) to 37 

 (G188); in 15-16, 21 (Gl57), 22 (Gl88), and 26 (G261). 



§ 321. The Periproct has a thickened rounded margin, coinciding in part with 

 the axial ridges of plates 7 and ] 2. The fossils lie in the rock in such a way that the 

 periproct is always to one side, though whether the natural position is to right or left 

 has not as yet been observed. The consequence is that the outline of the periproct 

 cannot be clearly seen, but it may be fairly well reconstructed from such specimens as 

 G143, G152, and Gl66 (text-fig. 50 ; PI. IV. figs. 49, 50, 55). 



§ 322. Traces of periproctals are seen in Gl52 (PL IV. fig. 55), where the largest 

 that can be measured has a greatest diameter of 7 mm. There is no evidence as to 

 the position of the anus, but I suppose it to have been towards plate 19, with a rectal 

 expansion towards plates 12, 7, and 8 (see further § 600). 



§ 323. The Tegmen consists in the first place of the five Deltoids, plates 20-24. 

 The internal cast of Gl87 seems to show that these met by sutures arranged on 

 the plan normal for quinqueradiate i^elmatozoa, viz. a triradiate suture at the oral 



