M. A. Pomel on the Classification of Echinida. 225 



Fig, 5. Bairdia formosa, seen from left side. 



Fig. 6. The same, seen from above. 



Fig. 7. The same, seen from the front. 



Fig. 8. Loxoconcha alata (male), seen from left side. 



Fig. 9. The same, seen from above. 



Fig. 10. The same, seen from below. 



Fig. 11. The same, seen from the front. 



Fig. 12. The same (female), seen from left side. 



Fig. 13. The same, seen from below. 



Fig. 14. Cythere crispata, seen from left side. 



Fig. 15. The same, seen from above. 



Plate XV. 



Fig. 1. Paradoxostoma (?) reniforme, seen from left side. 



Fig. 2. The same, seen from above. 



Fig. 3. Cytherura acris (male ?), seen from left side. 



Fig. 4. The same, seen from above. 



Fig. 5. Cythere favoides (male), seen from left side. 



Fig. 6. The same (female), seen from left side. 



Fig. 7. The same, seen from above. 



Fig. 8. Cythere Speyeri (male), seen from left side. 



Fig. 9. The same (female), seen from left side. 



Fig. 10. The same, seen from below. 



Fig. 11. The same, seen from the front. 



Fig. 12. Cythere dissimilis, right valve, seen from the side. 



Fig. 13. The same, seen from above. 



[All magnified 40 diameters.] 



XXV. — Observations on the Glas.sification of Echinida, to 

 serve as an Introduction to the Description of the Tertiary 

 Fossil Echinodermata of Western Algeria. By A. POMEL*. 



I HAVE had the honour to present to the Academy a series of 

 lithographic drawings representing some fossil Echinodermata 

 from Algeria, which are to form a part of the palaeontology of 

 that country. The descriptive part of the work is not yet 

 printed ; and I now submit to the judgment of the Academy 

 the introduction to this work, in which I propose certain mo- 

 difications in the classification followed by authors. 



The number of the series of coronal plates, sometimes 

 twenty, or two in each area, in the true Echinida, sometimes 

 much greater by their multiplication in the interambulacral 

 areas, and even in the ambulacral areas in the Tessellata, 

 gives a first division, of the rank of a suborder. 



The Echinida present three types, which advance regularly 

 from the bilateral to the radial symmetry, and which I 

 name Spatiformes, LampadiformeSy and Glohiformes. The 

 first have the mouth placed very eccentrically in front, and 

 the anus behind j the obliteration of the anterior ambulacrum 



* Translated from the ' Comptes Rendus,' Aug. 3, 1868, pp. 302-305. 



