85 
greater or less extent, of the anal and large azygous plate. It is not, 
however, caused by the introduction of these plates, as Sir P. M'Coy 
suggested, “ by the interj)olation of the large irregular intercostal . . 
. . . and the second costal.”^ 
A marked diversity exists between the descriptions of the form of the 
basal plates and those of the second ring, as given by M* *Coy and Wachsmuth 
and Springer on the one hand, and De Koninck and Patto on the other. 
De Koninck figured the anterior hasals as pentagonal — they are hexagonal 
as figured by M‘Coy, and described by Wachsmuth and Springer, — hut the 
left posterior basal as pentagonal, and the right posterior basal as hexagonal, 
Avherein he was right. The posterior basal De Koninck figured as hexagonal, 
Avhereas it is heptagonal. llatte Avas correct in his description of the anterior 
hasals as hexagonal, and the left posterior basal as pentagonal, but on the 
other hand, he called the right posterior basal hejitagonal instead of hexagonal, 
and the posterior as octagonal instead of heptagonal. By M‘Coy, and 
Wachsmuth and Springer, the description of these plates is correctly rendered. 
In the more recent nomenclature of Mr. P. A. Bather," the azygous plate 
of Wachsmuth and Springer becomes the radianal, or as the late Dr. P. II. 
Carpenter expressed it, a radial “that has assumed anal functions.” The 
anal plate is then termed by Mr. Bather the brachianal. The argument 
adduced by him in support of this change of nomenclature is too long for 
reproduction here, but a perusal of his remarks on the “ Anal Plates” in his 
paper on British Possil Crinoids ” ^ Avill well repay the student. I lia\"e, hoAV- 
ever, taken the liberty of reproducing his dissection of the anal region of the 
Tnhrachiocrinus calyx. The outline of the plates as given in his diagram 
in chief is strictly accurate. 
Fig. 3. 
* Ann. Mag. Nat. Hist., 1847, XX, p. 228. 
3 Ann. Mag. Nat. Hist., 1890. V (6), p. 333, t. 14, f. 35. 
* Ihid, p. 319. 
