145 



8. A. cordata. Cordato-conical ; assulae evident ; dented 

 in at the anterior part ; the ambulacra in bands, with four 

 rows of pores ; the vertex not divided. 



Spatangus ananchytis ? Leske ap. Klein, Tab. liii. fig. 

 1, 2. Fossil. 



9. A. spatangus. Cordated, convex; ambulacra im- 

 pressed and continued to the mouth ; a groove in the ca- 

 rinated posterior part. Fossil, from France. 



10. A. semiglobus. Ovato-hemispherical ; base flat ; am- 

 bulacra narrow, with ten biporous lines, approximated in 

 pairs ; the vertex undivided. 



Echinocorytes minor. Leske ap. Klein, Tab. xvi. fig. 

 C. D. Fossil. 



11. A. pillula. The least; ovato-globulose ; rather con- 

 vex beneath ; vent in the upper part of the edge. Fossil, 

 from near Beauvais. 



12. A. cor avium. Subcordated, convex ; ambulacra 

 widely striated ; the fifth obsolete. 



Spatangus ovatus. Leske ap. Klein, Tab. xlix. fig. 

 12, 13. Fossil. 



GENUS XIII. Spatangus. Gibbous, heart or egg- 

 shaped ; the mouth beneath, near to the wider end, trans- 

 verse, labiated, and without teeth ; the vent on the side, at the 

 opposite end ; the ambulacra, four or five, short and unequal. 



The striking difference of form between the egg-shaped 

 and heart-shaped species of this genus had almost induced 

 Leske to divide these bodies into two genera, and to have 

 considered the former as brissi, and the latter as spatagi ; 

 but further consideration, and the concurring opinion of 

 Muller, as to the identity of the animals themselves, led him 

 to retain them under one genus, separating them by di- 

 visions, chiefly founded on these characters, into the two 

 families of brissus and spatagus. Lamarck has thought 

 proper to effect this separation in a more simple manner ; 

 he divides the species into those which have four ambu- 



u. 



