KONGL. SV. VIOT. AKAOKMIENS HANDL. BAND. 19. N:0 7. 61 



bring out strongly the great contrast exhibited in this point by the Pourtalesiaclje. For 

 while these, in other regards, have not a little in eonnnon with the Spatangida-, and 

 share a few features with the (Jassidulida?, tliey diffei' widely tVoni either in being 

 homoiopodous. Their pedicels are all simple, and diti'er in size only, the phyllodean 

 and the upper frontal jiedieels being larger than the rest, wjiieh are very minute, 

 PL IV, fig. 16, 21, 22; VI, 40, 41; VII, .W. They all terminate in a rounded or 

 slightly tumid top, which, in some states, is surrounded by a narrow circular brim, 

 not unlike that of Rli) nchopygus, PL XI, fig. 11^, 119. The very dense pigment of 

 their tissues so obscures its structure that I could not even make sure of the existence 

 of calcareous spicules. The peripodia, PL I, fig. 5, 6, 7; IV, 15, 24; V, 27, 29; VI, 

 44; VII.I 47; XII, 149, not unlike those of the Cassidulidaj, are sunk, and the two 

 perforations confluent in the pliyllodean and frontal ones, separated in the minute 

 subanals of V b. In the ventral, subventral and latei'al plates of the ambulacra the 

 diminution of the peripodium relatively to the entire surface of the plate is carried 

 to the extreme, it being hardly discernible over the greater part of the ambulacrum, 

 and far inferior in size to the smallest of tubercles. The ambulacra are also all ape- 

 talous and perfectly even with the perisome, and all this, combining with peculiarities 

 of the interradial areas described above, tends to soften down the elsewhere salient 

 diversities of the two predominant systems, and to give to the whole surface of the 

 skeleton the character of smoothness, which the Pourtalesiada? have in common with 

 their fellow-habitants of the great depths, the Apetalous Spatangidae. 



IV. THE CALYCINAL SYSTEM. 



The homologies of the calycinal system in Crinoidea and Echinoidea. Tiarechiiius. Salenia. Its modi- 

 fications during geological development. Echinoconidae. Spatangidre. Its decay in the Fourtalesiadije. 



Years ago it occurred to me, as it had to others, that the general resemblance 

 of the )>apical» system in the Cidarid«, Saleniadaj and Echinidai, to the calyx of cer- 

 tain Crinoidea, might be a morphological fact of importance with regard to a true 

 perception of the homologies of the skeletal constituents in the Echinoderms generally. 

 For such is in reality the conformity betAveen the respective parts of both structures, 

 that, when once perceived, it must leave a strong impression of some hidden meaning 

 well worth understanding, and often enough it may have called forth reflexions that 

 far less often were recorded. Louis Agassiz ^) once remarked, as of peculiar interest, 

 ')the correspondence between the development of the calcareous central network)) of 

 the disk in the young »Startish and the stem of Pentacrinus»; the arrangement of the 

 five plates »surrounding it and those alternating with them that will form the five 



') Twelve Lectures on comparative Embryology delivered before the Lowell Institute, in Boston, December 

 and January 1848—49. Boston, Flanders & Co. 1849; p. 17, 22, 24, 26. 



