. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. the Crinoitlea, Cystidea, and Blastoidea. 261 through the pores and filled the tubes, to be aerated through the thin external covering by the surrounding water. In Caryocrinus the water passed inward, through the pores, into tlie tubes, ancf aerated the fluid within the general cavity of the body. The discovery that the fissures and pores of the Cystidea do not communicate directly with the general cavity of the body is entirely due to Mr. Rofe. After reading his highly impor-
. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. the Crinoitlea, Cystidea, and Blastoidea. 261 through the pores and filled the tubes, to be aerated through the thin external covering by the surrounding water. In Caryocrinus the water passed inward, through the pores, into tlie tubes, ancf aerated the fluid within the general cavity of the body. The discovery that the fissures and pores of the Cystidea do not communicate directly with the general cavity of the body is entirely due to Mr. Rofe. After reading his highly impor- tant pa])er, I re-examined a great number of specimens, and found sufficient to confirm his observations. 3. On the Genus Codaster. Every author who has described a species of this genus lias remarked the peculiar striated areas in the interradial spaces. Prof. M'Coy, the founder of the genus, pointed out their re- semblance to tlie hydrospires of the Cystidea; but it was Mr. Rofe who first showed that they were also identical in struc- ture therewith. On comparing one of these with that of the Cystidean Pleurocystites (fig. 5), we at once perceive that they are the same in external form, while Mr. Rofe's figures show that the section at ^fZ() has the structure of fig. 9, which only differs from fig. 5 h in being straight above instead of concave, and in being divided into two parts. This division is the result of the position of the arm, which cuts the hydro- spire in two in a direction parallel to the fissures. By draw- ing the j)oints d a and a d together, we get figure 10, which is, in general plan, a section across one of the ambulacra of a Pentremite. On examining nearly all the published figures of s]')ecies of this genus, I find that there is a series of forms wliich exhibit a gradual passage, from those w^ith the hydro- spires almost entirely exposed (as in fig. 8), through others, in Fi^. 8. Fio;. d Fig. 10. ^ %^1^. Please note that these images are extracte
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