400 Bibliography. 
ding several hundred figures. These descriptions are preceded by a 
notice of the external and internal organization, mode of growth, rela- 
tions to other Clypeastroides, and their geological position and distribu- 
tion. On comparing the fossil and existing species, well marked diffe- 
rences have been found to exist, and of the genera Mellita, Rotula and 
Encope, all the species belong to the actual epoch. It is also interest- 
ing to notice the fact, that among the Scutellz, as well as some of the 
other Echinodermata, the species beome larger and larger as we ap- 
proach the present period, precisely the reverse of what is true with 
regard to some of the Vertebrata, Mollusca, &c. 
Previous to the labors of Valentin, Tiedemann, Meckel and Delle 
Chiaje had already investigated the general anatomy of the Echini, 
but the microscopical examinations of the former into the minute struc- 
ture of the different organs, are almost entirely new. In many of the 
soft parts, such as the ambulacral tubes, buccal membrane, external 
branchiee, ézc. Valentin has discovered small calcareous bodies, assu- 
ming various shapes, resembling somewhat the spicula described by 
many recent microscopists, as existing in the Sponges, Alcyonias, Acti- 
nias, &c.* ‘* Why,” asks M. Valentin, “may not these minute parts 
be preserved in a fossil state, as well as the shell, the lantern, the teeth, 
and other organs? Iam convinced that the microscopic paleontology 
of the Echinodermata will become a vast field for research.” ‘The gen- 
eral organization of the shell, its microscopic structure, its mechanism, 
its appendages, and mode of increase, are all treated of in full detail, 
as are also the digestive, respiratory, circulating, nervous, and genera- 
tive systems. Scarcely any thing is as yet known with regard to the 
mode of copulation, although the duality of the sexes has long since 
been determined. Nearly every thing relating to the embryology of 
the Echini, yet remains a desideratum. 
The series of monographs of which those just noticed form a part, 
constitute one of the most important additions which have been made 
to modern zoology, no less in consequence of the completeness of the 
plan upon which they have been conceived, than the fidelity with which 
they have been executed. Jee 
* Prof. Bailey has suggested the possibility of determining the existence of the 
Actinie in the tertiary formations, by means of the minute spicula, which are the 
only solid parts. Quite recently I have detected spicula in the dorsal appenda- 
ges of the Eolis, which resemble somewhat those met with in the Actinia ; they 
are found in a small sack, recently described and figured by M. Quatrefages, though 
no mention is made of its contents, situated at the extremity of the appendage, 
Opening and discharging its contents externally. 
