1879.] NATURAL SCIENCES OF PHILADELPHIA. 251 



Axillary plates = plates between the divisions of the rays = in- 

 tersupravadials of Hall and other authors. 



Interbrachials = plates between the arm openings of each ray. 

 This term is not strictly correct, when taken in connection 

 with our definition of "brachials," but it has been long used 

 in this sense, and as no confusion is likely to arise, we think 

 it best to retain it. 



Anals = the series of interradial plates which support the anal 

 opening or tube. 



Apical dome plates = the system of plates in the vault which oc- 

 cupy a position analogous to that of the apical plates of the 

 calyx. They consist: 1, of a central plate at the apex of the 

 dome ; 2, of five large plates (there are generally four large 

 and two small ones, the two latter equivalent to one, being 

 separated by the anal area), arranged around the apex, inter- 

 radially disposed, and corresponding to the first radials; 3, 

 of five radial dome plates, alternating with the last, and corres- 

 ponding to the first radials. Wachsmuth, Ainer. J-ourn. Sci., 

 Sept. 1877, p. 187, called the first seven of these plates "api- 

 cal plates." This must be changed to avoid confusion, as the 

 genitals and oculars of Echini are designated by the same 

 term. We now apply the term " apical dome plates" to the 

 whole system of principal vault pieces. These plates, which 

 have no representation in the structure of the Stomatocrinoidea 

 nor Echini, exist in a greatly reduced form in the Blastoids, 

 but are specially characteristic of the Actinocrinidae, Platy- 

 criuidae, etc. The single plate at the apex we propose to call 

 the central dome plates ; the first ring of interradials surround- 

 ing it, the proximal dome plates, and the next ring radially 

 situated, the radial dome plates. 



Oral plates = large interradial plates, covering in form of a pyra- 

 mid the oral side of the Pentacrinoid larva (Wyville Thomson 

 and Carpenter) = consolidating plates in Cyathocrinus 

 (Wachsmuth) = deltoid pieces in Blastoidea. The term " con- 

 solidating plates" is discontinued. 



Hydrospires = certain organic structures in connection with the 

 inner walls of the test, composed of parallel tubes or folded 

 sacs, probably in connection with the water system. 



Respiratory pores or orifices = openings through the test, in 

 connection with the hydrospires, apparently for the introduc- 

 tion of water for respiratory purposes. 



