378 DR F. A. BATHER. 



are wanted, but the loss of flexibility is immediately compensated by the diminution 

 in size of the adjacent plates. 



§ 63. The Appendage. — Logically one should proceed to discuss the openings in 

 the theca, but their interpretation depends so largely on the interpretation of the distal 

 tapering appendage that the present order is more convenient. 



Examination and comparison of a number of specimens of D. Barrandei and 

 D. scotica, with a few of D. Sedgwicki, convinces me that normally this structure is 

 composed of four vertical columns of ossicles (see especially PL 11. figs. 14-18). The 

 ossicles in two adjoining columns are larger than those in the other pair of columns, and 

 these larger columns are towards the outer side of the theca : in other words, if the 

 fossil be viewed so that the appendage is to the spectator's left, and preserved without 

 distortion, then there will be seen two vertical series, a large one on the left and a smaller 

 one on the right. The words " large " and " small " are used here to express differences 

 of two kinds : in the Bohemian species the outer ossicles appear to be wider than the 

 inner ones, but both series are of the same height and general thickness ; in the Scottish 

 species, the outer ossicles are not so wide as the others, but they are notably thicker. 

 In the Bohemian species the inner series of one face does not alternate with the outer 

 series of the same face ; in the Scottish species, if the two series do not clearly alternate, 

 at least they do not seem to correspond, and certainly the two columns of the larger 

 and smaller series respectively do alternate with one another. In Z). scotica the suture 

 between the outer and inner series of plates may be impressed (PI. II. fig. 18). 



§ 64. A specimen of D. Barrandei (E 16028, PI. I. fig. 4) suggests that the outer 

 series may in some cases have formed only a single column ; the conclusions to be 

 drawn from this are discussed later (§ 100). 



§ 65. In all species there is a large lumen contained between the inner and outer 

 series of ossicles. There is, however, no trace of any opening from this lumen to the 

 exterior, whether at the distal or proximal end, or in the form of pores or of slits 

 between the plates. 



§ 66. The ossicles at the proximal end are generally more massive than those 

 forming the greater part of the appendage, and merge into the stouter thecal plates 

 already described (§ 61). One gets the impression that the ossicles of the appendage 

 have been gradually modified from thecal plates, and that there is less difi"erentiation 

 in the earlier species. The beginnings of the thickening of the ossicles are seen in 

 D. Sedgwicki in the form of transverse internal ridges strengthening the plates (? of the 

 outer series alone) (PL I. fig. 9 ; cf. PL II. fig. 16). 



§ 67. Barrande (1887, p. 74), relying largely on the opinion of Trautschold, 

 considered the appendage as a "tubus ventralis." At that time the appendage going 

 by that name in the Crinoids was not well understood. We now believe that it may be 

 either a simple anal (or more properly, rectal) tube with the anus at its distal end, or a 

 ventral sac containing an expansion, frequently a coecum, of the rectum, modified for 

 respiration. The discovery of the vent of Dendrocystis at the opposite end of the 



