446 



DR F. A. BATHER. 



posterior deltoid, because the pore or pores would have stopped its passage along the 

 suture ; therefore that groove, leading towards plate 18, probably had no more than 

 three or four brachioles. 



§ 326. It is not always clear whether the brachioles were borne by the actual thecal 

 plates of Circlets IV. and V., or whether there was what I have called a proliferation 

 of the deltoids — an intensification of the splitting described for deltoid 23, by which 

 separate epithecal plates were formed for the support of the brachioles. That this 

 may have been the case, at least to some extent, is suggested by the row of small 

 plates at the top of plate 19 in Gl33 (Plate IV. fig. 51 ; see also text-fig. 54). 



The brachiole-facet is rarely distinct. The best example is on plate 19 of Gl33 

 (text-fig. 56), and shows a faint fulcral ridge, separating the ligament-fossa from the 

 two muscle -foss£e, as depicted by Jaekel for Callocystis (1899, p. 90, f. 14c). 



Fio. 52. 



Fig. 53. 



Fig. 54. 



Text-figs. 52-55. — Deltoids and Food-grooves of Oheirocrinus constrictus. Sketches enlarged about 6 diameters. 



Fig. 52. — Plate 21 of G 261, with the proximal, i.e. adoral, region towards the observer. The convex curve of this region is 

 bounded by the main food-grooves The concave curves on the distal margin are due to the branches of the food-grooves, 

 which separate the proliferated brachioliferous elements (cf. PI. IV. fig. 52). 



Fig. 53. — The fjod-grooves that branch towards the curved margin of plate 15, in G157 (see PI. IV. fig. 49). A few cover- 

 plates are preserved. 



Fig. 54. — The main groove between the large deltoid 23, on the left of the drawing, and the medium-sized deltoid 20, at the top 

 of the drawing, bifurcates as it reaches the small deltoid 24, to the right of the drawing. The branch between 23 and 21 

 is continued round 23 by the proliferation of plates from 24, and between those plates it gives off' branches, each of which 

 ends in a brachiole-facet (not visible in the figure), making iive facets in all to this right posterior groove. These facets lie 

 above the radial plate 18. Between deltoids 23 and 24 some cover- plates are still seen, partly sunk into the groove. The 

 .sketch is made from G 145. 



Fig. 55. — The groove passing between deltoid 21 on the left and 22 on the right, towards radial 16, is seen broken up into 

 at least four grooves passing between brachioliferous plates proliferated from those two deltoids. A few cover-plates 

 are preserved. The vertical line on the left is the suture between radials 15 and 16. Specimen G 261 ; cf. 

 PI. IV. figs. 52, 53. 



§ 327. Impressions of the Brachioles seen in a few specimens (esp. Gl57, 

 Gl67, and G261) show that those organs had the normal biserial structure with a 

 distinct ventral groove (PI. IV. figs. 51, 53). The diameters observed are 7 mm. 

 (Gl57), "5 mm (G261). The greatest length from the theca attained by any 

 fragment is 12 mm. (G157). 



§ 328. The Stem in Gl57 (PJ. IV. fig. 49) is preserved to a length of 39 mm. 

 The proximal region merges so gradually into the median region that its length can 

 only be estimated arbitrarily as 18 mm., within which distance its diameter decreases 

 from 5 "2 mm. to 2'3 mm. In the 21 mm. of the median region the diameter continues 

 to decrease to 1 '5 mm. The more proximal visible columnals of the proximal region have 



