INVERTEBRATES. 201 



the lower side in the latter being obtuse. Second radials a 

 little wider than long, hexagonal, about one-half to two-thirds 

 as large as the first radial plates, and ranging a little more 

 obliquely outwards. Third radial pieces smaller than the 

 second, from which they extend out almost horizontally; cre- 

 nate transversely, their lateral extremities curving up to con- 

 nect with the vault pieces extending out over the rays, hepta- 

 gonal in form, and each supporting on its outer sloping sides, 

 one or two secondary radials, which also project out horizon- 

 tally. 



The first anal piece is nearly as large as the first radials, 

 about as wide as long, hexagonal in form, and supports on its 

 superior sloping sides two smaller pieces, one of which is hex- 

 agonal, and one heptagonal ; above these there are in the next 

 range four smaller pieces, which connect with the vault pieces 

 above. The first interradial plates are about the size of the 

 second radials, as long as wide, hexagonal and heptagonal, and 

 support two or three smaller pieces in the next range. 



Of the distinct radiating costse on the first radial plates, from 

 three to four pass across to the sides by which they are con- 

 nected together, and from each to the base, while one or two 

 extend to the margins connecting with the second radials, and 

 first interradials above. The third radials are somewhat con- 

 stricted at their connection with the second radial pieces, and 

 more or less tumid above, but have no distinct costse. Height 

 to top of third radial plates, about 0.65 inch; do. to top of 

 vault, near 0.95 inch; breadth of body between the rays, 0.90 

 to 1 inch ; breadth of base, from 0.42 to 0.45 inch ; height of 

 do., 0.12 inch. 



This species is somewhat allied to A. stellaris, de Koninck and Lehon (Eech- 

 eaclies sur les Cri?wides, Belgique, pi. 3 and 4), but has a more depressed summit, 

 and more convex sides below the arms; while its first and second radial plates, 

 and first interradials, are larger and more convex, as well as much more strongly 



26 Sept. 3, 1866. 



