PLATE XXIII
1. A Stephanastrum , with the four central arms similar to those of Stephanastrum Rhombus of Ehrenberg, enveloped in a circular spongiose web, beyond which extends an irregularly- spinous transparent siliceous border , which also extends round the ends of the arms. I think this round web is the normal form of the Stephanastrums and Rhopalastrums , and the key to all the curious
3, 4, 5, and 6 sided cushions; the number of arms deciding the number of sides, and stretching out the web in the course of growth into the various shapes as long as it remains attached to them ; in slide " Chimborazo Barbados Rd." size .0228 .
2. Resembles Placolithes Radiata . Mikrogeologie Pl . XXXIV, fig . 5. There are two valves , the upper one plaited like a fan. I have since seen a broken specimen in which the plaits appear like tubes , hollow, like the beautiful raised ribs on the African Cardium Costatum. Dr. Wallich confirmed the notion of the fan-like plaits, by detecting a crack across one of them.
3. A lovely transparent cross, with doubly trifid ends ; possibly a sponge spicule ; in form most nearly resembling some of the spicules of Hyalonema Mirabilis , on Taf. III . of Professor Max Schultze's "Beitrage," & c.
4. A transparent Plate, irregularly three-lobed , each lobe bifurcate, in slide " S.P. Barbados ." Material from Dr. Kingsley. It appears to be of the nature of those " Hex-radiate plate- spicules : depicted by Dr. Bowerbank as from a " Euplectella."
5. An explanation of mode of growth of fig. 5 on Pl. VII. A Dictyochus net?
6. A Rhabdolithes, giving a curious example of the way the siliceous outshooting spines seem to go wandering on wherever they find the least obstruction; at ' a ' there seems to have been an intended change of course, checked. The extreme flexibility of these spines might lead to a supposition whether there might not be combined with the silex in their composition some portion of the keratode (or horny matter) stated by Dr. Bowerbank to enter into the formation of even the Siliceous sponges , or to line the siliceous coating of the spines.
7. A double circlet of Acanthodesmia of Müller. A single circlet is given on Pl . 11, fig. 6. Barbados earth.
