Prof. Agassiz on the Echinodermata, 193 



monograph which it is my intention shortly to pubHsh upon 

 the hving species of the genus Echinus (Auct. Antiq.) I have 

 estabUshed the following divisions, of which I here only in- 

 dicate the typical species : Temnopleurus (Ech. toreumaticus), 

 Pleurochinus (E. bothyroides), Microcyphus (E. versicolor), 

 Tripneustes (E. ventricosus), Amblypneustes (E. griseus). Tax- 

 opneustes (E. pileolus), Stomopneustes (E. variolaris). I have 

 also thought' it better to form three subdivisions of the genus 

 Arbacia, restricting that name to the small fossil species, and 

 proposing that of Tragypus for the species whose anus is 

 closed by a valve of four pieces, and that of Agarites for those 

 which have the interambulacral areas partially destitute of 

 tubercles and spines. 



The Holothuri(B are'always the division of Echinodermata in 

 which there remains the most to be effected. The difficulty of 

 observing these animals has hitherto not enabled the science 

 to be supplied with designs [planches) sufficient for its exi- 

 gencies. There are none but those which are published by 

 MM. Quoy and Gaimard in the ^ Zoological Atlas of the As- 

 trolabe,^ and which, as it regards their execution, do not leave 

 anything to be wished for ; but as it respects their distribu- 

 tion into genera, a great deal too much of vagueness and un- 

 certainty is presented by the characters selected as the basis 

 of the groups. 



Oken (Lehrbuch der Naturgeschichte, 1815) was the first 

 to divide the Holothurice into four genera, which he calls Thy- 

 one, SubuculuSy Holothuria and Psolus, Lamarck only ad- 

 mits two genera in this family, the Holothurics and the Fistu- 

 larim ; these genera again are not well determined. Cuvier, 

 without giving generic names to his divisions, has nevertheless 

 established, in the first edition of the ^ Regne Animal,' six very 

 natural sections in the genus Holothuria, the first of which 

 corresponds to the genus Psolus of Oken, the second to the 

 genus Cuvieria of Peron, the third and fourth to the true Ho- 

 lothuria, the fifth and sixth to the genus Subuculus of Oken, 

 which is also synonymous with the genus Cucumaria, Auct., 

 or Pentacta of Goldfuss ; lastly, the sixth corresponds to the 

 genus Thyone of Oken, which Mr. Fleming has named MUU 

 leria in his ^ History of British Animals,' but which is not the 

 genus Millleria of Jaeger. Eschscholtz subsequently esta- 

 blished in the ^ Zoological Atlas,' after the second voyage of 

 Capt. Kotzebue round the world, two new genera under the 

 names Synapta and Chisodota, which correspond to the genus 

 Tiedemannia of Leuckardt (Isis, 1831, Compte rendu de la 

 reunion des Naturalistes Allemands a Hambourg). M. Leuck- 

 ardt has also established the genera Phascolosoma and Oche- 



