IN 1892 F. Jeffr. Bell in his paper on the classification of the Ophiuroids*) 

 described under the name of Ophioleresis elegans a very remarkable Ophiuroid, 

 differing from all other recent Ophiuroids in the complete absence of ventral piates ; 

 further the dorsal piates are stated to be "definitely double", and the side-plates, 

 instead of lying flat against the side of the vertebræ, are wider than long and stand 

 out from the sides of the arm. The vertebræ present an "extremely generahzed 

 condition", without knobs and pits, the recesses on the adoral side being excessively 

 shallow and, in correspondance, the articulating elevations on the aboral side very 

 slight and inconspicuous. 



"From this simple form differentiation would seem to have preceded along two 

 lines ; there has been an increase in complexity of artirulation, associated with the 

 fixation of ccrtain ossicles and spines, or there has been vegetative repetition and 

 branching with a more primitive inconstancy and irregularity of anatomicai char- 

 acters" (Op. cit. p. 179). Ophioleresis is thus regarded as representing the most 

 primitive type of Ophiuroids, from which have developed along one line the Astro- 

 phytids, along another line the rest of the Ophiuroids. These latter are divided into 

 two groups, according to the structure of the vertebræ, viz. the Streptophiuræ, with 

 the vertebræ articulating "by means of a more or less simple ball-and-socket joint", 

 and the Zygophiuræ, in which "the movement of the ossicles on one another is 

 limitcd by the development of lateral processes and pits". 



These results of Bell'b researches have met with great approval. The division 

 of the Ophiuroids into Zygophiuræ and Streptophiuræ has been adopted by J. VV. 

 Gregory in Ray Lankester's "Treatise on Zoology" III. Echinoderma, 1900, as 

 also in the same authors paper "On the classiflcation of the Palæozoic Echinodcrms 

 of the group Ophiuroidea"*); by Meissner in Hamann: Schlangensterne, 1901, in 

 Bronn's "Klassen und Ordnungen" ; by Delaoe & Hérouard in "Traité de Zoologie 



') F. Jefprby Bell. A Contribution to the Gassiflcation of Ophiuroids. with DescripUons 

 of some new and litUe known Forms. Proc. Zool. Soc. 1892. p. 176 183. PI. XI— XII. 

 •) Proc. Zool. Soc. 1896. p 1028. 



