684 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxii. 



of dorsal surface are rather numerous and are of several sizes, but all 

 smaller than the ventrolaterals. Pedicels of mid-ventral region small 

 and fnconspicuous, and frequently more or less completely retracted 

 into body wall. 



Radial pieces of calcareous ring- considerably larger than interradial, 

 posteriori}" rather deeply excavated, the anterior border with three 

 notches, the central the deepest (lateral ones sometimes very small). 

 Interradials are not excavated posteriorly, and have a prominent tooth 

 anteriorl3^ Madreporic canal runs forward in the dorsal mesentery 

 and gradually upward, the madreporic body being fastened to the 

 body wall at the anterior edge of the mesentery. Polian vesicle single. 

 No tentacle ampulla^ extending into body cavity, the rudiments of 

 these merely occupying the space in front of the calcareous ring. 

 The "ampulla" on either side of the anterior tooth of interradial 

 piece is much larger than those of radial pieces, as in preceding- 

 species, in consequence of difference in size of the component parts of 

 calcareous ring; but there is no corresponding difference in size 

 between the tentacles. Gonad forms a large tuft on left side of 

 mesentery. Respiratory tree well developed. Intestine follows a 

 simple S-shaped course. Longitudinal muscle bands rather small. 



The disks of the larger tables of general perisome have a width of 

 0.135 to 0.18 mm., and the spires a height of 0.10 to 0.15 mm. In 

 outline the disks are often fairly regularly scalloped (Plate LXXI. fig. 

 lA), especially when there are no secondary perforations. The 

 primary peripheral holes are always larger than the central and are 

 commonly ovate in outline, or subcircular. The secondary perfora- 

 tions arc formed by the forking of the spokes separating the primarj^ 

 holes. The framework of disk is rather delicate, the spokes being- 

 heavier than rim. The spire flares more or less toward the summit, 

 and the three rods terminate in two (sometimes three) irregular den- 

 ticulate prongs; or the prongs are occasionally obsolete. The amount 

 of divergence of the terminal portion of rods and the distance between 

 their tips and the point where the three meet is subject to some small 

 variation, the figures showing two typical examples. (Plate LXXI, 

 figs. Iff-^.) The distance between the disk and crossbeam is alwa3^s 

 less than the distance between the latter and the point of divergence 

 of the crown prongs (which depart from one point, as it were, since 

 there is no hole between them, as is usually seen when viewing a table 

 from above). In the walls of the pedicels the tables are small and 

 irregular, as well as variable, man}" of them lieing reduced to lowest 

 terms. The disk is a simple ring (no peripheral perforations) from 

 which arise the three spire supports, which commonly terminate in a 

 cluster of blunt teeth or in one or two sharp ones. The teeth are 

 scattered along the side of terminal portion of the rod. Terminal 

 plates of pedicels vary in size. They are simple circular jiei-foratcd 



